[bmm6o]

Does it matter how long destroying the universe takes, since that's in the unsorted branch? The universe with the sorted list continues immediately, the cleanup is handled elsewhere.

[WJW]

I suppose it would depend on if your multiverse has stop-the-world GC or can do it concurrently.

[bmm6o]

The GC pauses clocks, too. There's no way to detect a pause from inside the universe.