The math is like a cycle with a biggest barrier for governments to shut down Bitcoin, is its design which is decentralized and open source. Everyone can reproduce Bitcoin node and run it to decentralized the blockchain from Bitcoin open source code, and the Bitcoin community are free to choose what chain they want to support and use.

Governments can do similar things like some teams that tried to fork Bitcoin, and succcessfully create many Bitcoin forks that are dead and are going to be dead coins.

https://forkdrop.io/how-many-bitcoin-forks-are-there

When you put it that way, it is of course immortal because it is not possible to shut it down or centralize it or censor it or ... but Bitcoin is technology and like any other technology it has its limitations. I believe eventually Bitcoin will be replaced with newer and better technology. It won't happen any time soon though, maybe 10 to 20 years from now we see something better come along... specially with the way technology is advancing which is speeding up.

In terms of supply, it's not immortal, it has a limit of 21 million and it will be last mined approximately in 2140.

But if we look at it, maybe even if all have been mined, obviously there will still be a lot of holders that are not going to sell. Although we really don't know what the future will be because it's obvious that we are unalive by that time. It could be that one one is using it, or everyone is still with this technology after 100++ years.

Nothing can completely shut down a decentralized network since there will always be miners keeping it alive, ensuring transactions continue. However, if Bitcoin were to be banned globally, it would definitely slow down its adoption, who would risk using it if getting caught means jail time? In that scenario, Bitcoin would likely go back to being mostly used for illegal activities, as those users aren’t worried about breaking the law in the first place.

Bitcoin is truly immortal Because no government can control or destroy it, Bitcoin is a decentralized coin and no one has the power to destroy it, and Bitcoin will keep growing more in price, some set of people refused to invest in Bitcoin because they believe a time will come when Bitcoin will drop and will lose value but that's not true Bitcoin can never lose value, Bitcoin has a limited number so no one can print more Bitcoin the number will forever remain as it is, so Bitcoin will become more valuable, with the way Bitcoin is going now a time will come to buy Bitcoin will become more hard, because a lot of people would have bought Bitcoin and hold, right now countries are now buying and holding Bitcoin for example El Salvador they where the first country to adopt Bitcoin as legal tender, holds around 6,002 BTC, valued at about $575.9 million also Ukraine has accumulated approximately 46,351 BTC, valued at around $4.4 billion, and UK holds around 61,000 BTC, valued at about $5.9 billion, however is from law enforcement seizures, and more countries are planning on buying and holding, so a time will come where Bitcoin will become more valuable and since no government can control or destroy it a lot of people prefer such investment.

Large reductions in global mining speed would create the danger of the next difficulty adjustment taking prohibitively long. Chances are that people will fork the blockchain then, but who knows at what price to the community.

If the government can find a way to shut down Bitcoin, which has 65K nodes and almost 21K are running, don't you think the government will be able to shut down a similar program that just started again? Personally, I don't think the government will agree and start hunting all these 65K computer users to shut down these nodes. They even couldn't find hundreds of them.

If the world cannot be united to stop these wars and help the poor people who are starving, do you think the whole world will be united to stop the internet and shut down Bitcoin? I don't think so.

Most of the bitcoin copies (at least Bitcoin Forks) failed to bear much less than bitcoin, so bitcoin failed to be decentralized that may not eventually lead to its value to be zero, but we will inevitably not see a similar model in the near future or that the use of bitcoin code again will not lead to creation A decentralized currency such as bitcoin.

Is it still Bitcoin, strictly speaking? Or is it already a copy?

Either way, it is immortal in that sense. But the same reason that makes it immortal might be the same reason why it becomes pointless in the end. If a government somehow controls Bitcoin and some supporters don't disagree, and decide to take a copy with a different set of rules, there might be many Bitcoin in the end. Precisely like what's happening today, only worse.

Every country might end up having its own version of Bitcoin. One country might not accept the Bitcoin of another country. That would make everything pointless.