CEX collapses don’t result in the destruction of the coins they hold. It’s usually due to a hack/theft or greedy/risky investments of customer funds.

Practically speaking, coins proven stolen from a CEX are "blacklisted" on most of the other exchanges where crypto interfaces with fiat. If you happen to come into possession of coins that originated from a "blacklisted" address, you will have to prove that you obtained them legally.

So yes... a majority of stolen coins are for all intents and purposes, "burnt". Will the major exchanges care about coins stolen from a CEX 10 years ago? Probably not, but I guess we will cross that bridge when we get to it.

Of course, it is possible to "tumble" these coins, but it's an arms race between criminals and chain analysis, and while they can evade the analysts in the short-term, the crime is recorded in a distributed ledger for eternity allowing near unlimited opportunity for future review.

I keep being told by maxis that P2P crypto->fiat is alive and kicking. Looking at recent hacks (Axie, Crypto.com, etc) seems like tumbling is quite doable too.