This wall of  text is terrible to read. Learn to break lines please.

You can't predict what the price of bitcoin will be next month, how can you predict 50 years? 100 years?

You can't know how much miners will receive when fee is the only reward. Probably, it will be enough. Miners are making a lot of money now, there is nothing to worry about them for now.

It's a well-known problem and there's no good solution as far as I know.
And it gets worse with solutions like the Lightning Network, which are helpful indeed in terms of sending txs at a very low fee, but (if successful) they would reduce demand for on-chain transactions.
Having a permanent bottleneck is also not a fix to the problem, as it would mean that sending bitcoins on-chain is unreliable as you wouldn't have guarantee that your tx will get confirmed in a timely manner even if the fee is high.
I believe the original idea was that there were meant to be many transactions with affordable fees, but that concept didn't quite account for the blockchain size issues.

Anyhow, I wouldn't worry about that too much as we still have a lot of time to sort that out. In a worst case scenario, we could change the algorithm, or hope that bitcoin related businesses will take on mining on themselves, as they have vested interest in keeping the network alive.

This question always comes up during halving period and the answer is always let’s wait till then. Many have worried in the past that at a reduction like this it wouldn’t be profitable but still we have miners. What will happen is miners who finds out that the process isn’t beneficial or profitable to them again will definitely quit, should it be large computational power that comes down then the difficulty target also reduces thereby inviting more miners too again.

As for the concern of whether the network will be decentralized I think yes the only concern will be if the mining nodes each decide to censor transactions they pick but maybe a node will try to harm the network carry out an illegal transaction? It will not happen because there would still be need for consensus

The real question is how much security we need? Bitcoin was less secure 10 years ago when hashrate was a fraction of what it is now, yet it didn't get attacked. It could be true that transaction fee rewards are sufficient to secure the network.

Also, there's another variable that almost everyone overlooks. Number of confirmations. If the network is more likely to get 51% attacked, then those who who accept transaction can just require higher number of confirmations. Today we used to treat 1 confirmations or 3 confirmations as secure, in the future it might be 10 or 20. No one is going to pay for coffee with on-chain BTC anyway.

Im not sure but I believe this is a good question. back then bitcoins market cap was probably only a few million so making an attack wouldn't be worth the effort. but now the market cap is 2 trillion, which is probably a million times higher which means the hashrate would need to be a million times higher to have the same security to value ratio as 10 years ago.

So security of the network should be proportional to the total value of it or the total market cap of bitcoin.

Also I think It would be better to look at the energy consumption of the mining network instead of the total hashrate because the hashrate increases from more miners and improvements to mining hardware. So looking at energy consumption cancels out the hardware improvement factor and would give a better estimate of difficultly to pull off a 51% attack.

If energy consumption of the network remained the same hashrate would still go up giving an illusion of increased network security.

I agree with you rigs are definitely getting more efficient with energy consumption but that efficiency gain doesn't help secure the network by itself. In theory if an attacker had the same hardware it would boil down to who has more available energy, the attacker or the network.

This is not true. The fee market and the demand curve will always have a point of saturation where additional fees and demands doesn't increase the total revenue. Lightning network is absolutely needed to offload some of it on the second layer while still maintaining on-chain settlement.

The cost is related of the revenue of Bitcoin mining, and thereby if your revenue of the miner drops, then the cost to attain X% of the hashrate decreases proportionally. The simple logical way of thinking is that miners won't mine at a loss and a drop in revenue equates to either a scaledown in operation or a slower growth. Even if your efficiency of ASIC gets ridiculously high, the cost of them would be a key factor in whether Bitcoin gets attacked or not.

In addition, we go through this so-called renewal of ASICs when newer ASICs are released. Miners will not purchase them unless it makes sense, ROI is better than the current ASICs and that all of the scrap and cost overheads are accounted for.

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Block size increase, increased in demand for blockspace, etc. These are the key factors to consider. If Bitcoin doesn't go mainstream by the time coinbase rewards goes to negligible, then it would be an issue.

fees (amount of sats) per transaction DOES NOT need to increase. they actually need to decrease

reasons:
a. the spot price per sat can increase to pay miners bills
b. the amount of transactions per block should and can and need to increase

by having more transactions and a better spot price per sat will incentivise miners, without making bitcoiners stop using bitcoin
by having more transactions per block means people individually can pay less, thus about to stay active, whilst giving a total tx income per block a boost
however
by having individual bitcoiners pay more and have less ability to transact will cause more centralisation due to lack of use of bitcoin due to limited transactions and costly transactions

miners are not paid per transaction. they are paid by total per block. so allowing more transactions is a better solution rather than enforcing individuals pay more and limiting how many transactions can be made, further pushing those remaining active to pay even more

analogy:
a rail-train operator does not increase profits, efficiency of passenger transport by removing economy seating of 60 chairs per carriage. replacing it for 6 business class chairs that are only reserved for the furry/cosplay convention
instead they extend the carriages to have more seating to allow more passengers to frequent the trains and get more income via the popularity of passenger transport(their purpose) via lower priced tickets individually but benefits by higher total income per carriage due to it

..
and please dont be idiots to respond that bitcoin then needs to suddenly jump or leap to millions of transactions a second.. thats just a stupid extreme fearmongering absurdity of huge numbers that dont even mean anything.. said just to ignore rational scaling.. (scaling does not mean sudden massive leaps)

as for your math

a 4mb block is 4000000bytes
if fees are 25sat/b = 100,000,000sat (1btc)
if 1btc=$250k then a block gets $250k not $62k
which over a day(144 blocks)=$36m not $9m

you also say 25sat/byte
where currently there is a average of 4000tx per block (1kb/tx)
so individuals pay 25,000sat per tx, which assuming your demo of 1btc=$250k 25,000sat = $62.50 per tx average
if fees go to 650sat/b so individuals pay 650,000sat per tx,  = $1625 per tx average
people just wont want to use bitcoin if tx fee were $62.50 each minimum with your assumed tx fee increase to $1625

a dynamic size that has upper and lower limits that adjust..
um going down in size is harder to control as you then have to do silly mile stones of accept 4mb upto X blocknumber(height) then only accept 3mb upto x block number if you want the size lower limit..

its much easier to just SCALE(slowly progress) in a upward way not a constant yo-yo up and down.. and when i say scale(slowly progress) in a upward way.. no its not leaping to millions of megabytes in a month... and no its not move to a small increase once a decade

but it doees mean doing things like each difficulty retarget.. where every Xfew months, year or halving move forward based on high % fill per block over X blocks as the decision maker where code sets the blocksize target growth.. not dev politics of having to code and adjust milestones every so often manually
EG if 52500 blocks(1 year) =X gb(of Y gb(95%)) then increase blocksize by Z%
whereby current would be x=200 y=210
where the code itself keeps the variables re-targetting/updated and not need devs to manually dictate/decide the next adjustment next year