In which case you're no longer using the GC. You don't have GC & deterministic destruction, you have GC xor determinism.

That case isn't completely deterministic the way stack is: for the stack you just shift the SP which is constant time, while heap allocation and deallocation require manipulation of a small database, possibly including a system call.

This is a bit of hair splitting I admit.

It is as deterministic as RC algorithms, which is usually the point being discussed.

Yep, splitting hairs. :)