It would be the same as in any language with manual memory management, you'd simply get a dangling pointer access. The 'move-by-default' semantics of Rust just makes this a lot trickier than in a 'copy-by-default' language though.

It's actually interesting to me that the Rust borrow checker can 'simply' be disabled (e.g. no language- or stdlib-features really depending on the borrow checker pass) - not that it's very useful in practice though.