Yes, it's a well known fact that opinions can change. And yes, there's certainly a tiny subset of euthanized individuals who would regret their decision if they were still around to regret it.

When it comes to bodily autonomy, we generally strongly err on the side of respecting one's "opinion at the present time" vs. "the possibility of a different opinion in the future".

What is the intent behind your statement? Are you suggesting that we deny people bodily autonomy "just in case"?