Casual investors will immediately drop BTC, same with institutional investors, most Bitcoin businesses would close. The only people left on the network in the US would be cypherpunks, criminals, and buyers of illegal services. On a global scale Bitcoin will suffer from a huge crash, easily 90-95%, because if the US would ban BTC, many other countries would follow. If the EU would also ban, it would effectively be a worldwide ban, because most of Bitcoin traffic comes from the West, and the West is very influential, plus eastern countries already don't like BTC and are talking about banning it.
Without enough hashpower Bitcoin would be easier to attack, which puts yet another instance of selling pressure on it.

In the end, Bitcoin will not die, because it''s decentralized and it can't be killed, but for most people it would be as good as dead, law-abiding citizens wouldn't want risk dealing with BTC.

If that ever happens, I expect many to go underground. Some crypto enthusiasts might even migrate to other countries where bitcoin is legal. Traders will most likely dump their holdings also. I don't about hash power.

This will happen

https://en.wikipedia.org/wiki/Executive_Order_6102

People will not give them their bitcoin though, and they can`t come into your house and seize it without your password like they did in the past to gold.

What will happen is there will be a big revolution if they are stupid enough to do such a thing, like this moron suggest.
https://www.youtube.com/watch?v=Cnz2oo8MRas (notice the stumble at 7-8 seconds)

In other words, nothing will happen, people will just exchange it for other altcoins or other fiats and just p2p trade it if they ban the exchanges. If they start to jail people for free trading I am sure the people will start to take heads.

Bitcoin can't die but what would be its use if most of the people who are into it right now will stop dealing with it? Virtually, it is going to be dead just like any good product that finds no critical size of a market. Now, using the scenario above, can we then conclude that the "life" of bitcoin is at the fingertips of the government? Though, of course, I don't expect the USA government to do what China did in 2017.

First off, this law would be challenged in the courts, so it would likely not be implemented any time soon. But assuming the law were somehow put into place and approved by Congress, it would have a severely negative effect on bitcoin in terms of price and network activity. There would be an underground market, obviously. I suspect most Americans would sell their bitcoin to the government or whoever is willing to buy it. Perhaps seeing the antagonism to bitcoin, China and Russia would consider it an alternative to the U.S. dollar, thus possibly offsetting the impact of American prohibition.

Bitcoin would still be around, however.

I am not sure what happened to the price because the bitcoin price does not just move because of one action. It will move from what traders demand and supply. I think that will happen too with the hash power, maybe it will reduce for a while, but that will not affect to the most hash power because we know that the mining process is not just come from the US. There are many other countries will still mining bitcoin, and if the US make bitcoin illegal, we don't have to worry about that. The recover will always happen, but we don't know how long it will recover, and bitcoin does not depend on one or two countries but it depends on how people use bitcoin itself.

It would certainly create some panic, but that is just a temporary panic.
I really don't see they will make it illegal as I believe they are pro crypto and this technology could help the economy of a certain country.

Bitcoin has been banned by some countries, but it's still here, kicking and alive, it dump and almost died but it recovers.
I guess BTC is one of the strongest investment due to its capability to recover in time in terms of value.

What will happen if US government chooses bitcoin as their reserve currency? And what will happen if US government advises all citizens to buy bitcoin and secure their future and that of their future? Well if what you say happens, I see many bitcoin either relocating from USA or adopting another country's citizenship. True, USA government will be pro bitcoin.

Price of bitcoin would crash since US has a huge influence on bitcoin's market and people would be panic selling creating a massive dump that would worsen the crash.

The Blocks produced per day will decrease. Here is a link about a similar topic where what if the hash rate drops. :https://bt.irlbtc.com/view/232325.0

It could take months for bitcoin to recover. but as long as there are miners to mine the blocks bitcoin will eventually recover.