Or until someone notices...

All the balances and stuff are public on the blockchain. It only takes one person to write a script to verify that the locked up amount matches the number of tokens out there. and when it doesn't, alert.

That then means any attacker will have to be very quick with their theft, and if so, there is still a good chance whatever coins they get will end up blacklisted or the transactions reversed by a sufficiently large army of upset users who fork the eth network or the L2 network.

Just get the ETH into Tornado Cash ASAP, that should avoid any potential blacklisting.

I mean even if you got it in there after blacklisting, how would they know the wallet that received it?

The folks at Optimism would certainly hit the pause button on that withdrawal before it escaped, if there aren't already limits and automatic controls in place. It takes 7 days to withdraw L2->L1 via the standard bridge.

(They have administrative controls for now during development, at some point they're supposed to turn it completely permissionless...)

You don't have to use the standard bridge though; I've withdrawn in less than five minutes using the Hop bridge/network, which I think just involves an additional fee to a middleman (my L1 transaction for it shows it spending ~0.02 ETH). I can't speak to what additional checks that protocol may have that would have prevented conversion of excess OETH though. Here's the FAQ for it:

https://help.hop.exchange/hc/en-us/sections/4405172442509-FA...

Edit: O...kay? Apparently the parent of this comment is aware of alternate, much-faster ways of withdrawing L2->L1, and what their constraints are, but still elected to leave those out and imply the one-week lag was a binding constraint?

(Would have posted as a reply, but my comment rate is getting throttled for some reason.)

I've used Hop too. Transfers are naturally limited to however much liquidity Hop has, though.

Edit: Sorry for being disingenuous and unnecessarily curt in my reply. I didn't mean to. I'm in some kind of weird zombie mode this morning.