In the past Bitcoin has done all sorts of crazy stuff. Going up 50% down 30% up 150%. All sorts of crazy things. It has even gone down 94% from ATH. Yes, crazy as it sounds. It has done this. Since Bitcoin's ATH was roughly $19,000, a 94% drop would equal about $1,140. I really hope this doesn't happen, but it could. This is probably a worse case scenario. (Well worse case scenario is it going to near $0, but this is a very very low probability imo).
Look at the bright side, then. It won't ever go below $1,000 again!

I have my doubts that we'll ever dip below the $3,000 level again, but it's true, it's a honey badger in both directions. Bitcoin (and markets in general) tend to push further in both directions than you can imagine. Best to be ready for it.
90% is too much, even for the worse crash in BTC history, no asset would devaluate that much, it could only happen if 50% of the holders sold
No, it would take
much less supply than that. Look at the order books of the major exchanges. They are thin as hell! That's why the markets are so volatile.