For example, Coinbase was founded in 2012 and is still doing well to this day, so not every exchange is going down.
Maybe not yet, they waiting us off guard.
That's such a paranoid outlook although I can share the sentiment, I won't worry too much about my bitcoin lest it's in the whole number or 0.1 territory about the security, probably don't use obscure exchanges and online wallets to store your coins.
Not storing your bitcoin in an online exchange is what people should do or what we should recommend especially to newbies. As what op name is "not your key not your btc" explained a lot already. Think about accessing the wallets that contains BTC without the private key or seed phrase is impossible to do so that's why not your key not your btc is a good saying when it comes having some btc in a wallet.