Q: Should I sell Bitcoin when its downfall?
A: Never, Never do that.
It depends on your reason to sold your Bitcoin, if you're sick or you need to pay your college fees, are you really want to hold Bitcoin and still sick or you quit your college? of course it's better to sold some of your coins to cover your cost.
Q: Is Bitcoin dying after FTX fall?
A: The Bitcoin price has continued to shrink in 2022 since Terra Luna initiated a significant crypto crash in Q1 and now FTX saga. Bitcoin will most likely have value and regain. The only thing that can make Bitcoin valueless is if all governments ban it or render it illegal. However, this consensus is almost impossible to reach.
There's no relation between Terra Luna and Bitcoin, it's off topic.
Even all governments ban Bitcoin, it doesn't stop someone to buy or sell Bitcoin. We have non custodial P2P marketplace and decentralized exchange e.g. BiSQ, so you can hide from government laws.
My question to you Q: What is your price prediction for 2023?
No body knows, just like someone can't predict when Binance will collapse just like Mt.Gox and FTX.