In countries where crypto is "banned" (illegal for mainstream use), do you think people will still use it? In such an scenario, it's possible on-chain criminal activity (mainly money laundering, terrorist financing, etc) will rise. To prevent detection, it's likely both criminals and average people will use a privacy-oriented coin such as Monero or Zcash. Bitcoin will be the least used cryptocurrency due to its transparent design. But I could be wrong.
I think that people will just start getting more cautious, from using their own nodes to mixing or coin-joining their money.
Also keep in mind that people use Bitcoin more as an investment than as a currency, and dormant money in a wallet is pretty low profile actually (until you move to sell it, that is).
Monero? Yeah, it's cool, but I'm unsure on how largely it's being used. And even if it had a great year... it's still far from its ATH vs Bitcoin.
What do you think? Will people still use crypto in a country where it's prohibited to do so? Or will they be afraid? What if all of the world's countries turn against crypto (which is very unlikely atm)? Will market prices go all the way to $0?
Your question is a bit strange in a world where crypto is starting to become mainstream, actually.
However, while prohibiting them is indeed a blow from the average Joe's point of view and some will leave the ecosystem, that's for sure, if the coin has a strong user base (and it is indeed useful) then the impact will not be so big - of course, it depends on what country/countries ban it. Some will keep using it no matter what: I know that Monero, although delisted by a huge lot of exchanges, is doing rather good; I've read here and there sparse stories about the use of Bitcoin and altcoins in countries they are banned, but people use them as separate income or investment because they have to,... keep in mind that people are much more resourceful than the governments.
But the world is bigger than a couple of countries, so the market going to 0 is usually not to happen. But it depends a lot on how strong the coin is.