Well, n0nce it looks like you solved my dilemma. Who would've thought it would've been a simple answer like that. I was quite enjoying my thought experiment. It's probably the best idea to leave a note, especially if you know that you aren't going to take anything from that wallet regardless how long. I don't think everyone that stumbles upon it will have that thought process though. I know some users would consider it a donation, and wouldn't think twice about it. Then, you probably have users like me who will overthink the process.

It does somewhat prove though that lost Bitcoin in this type of situation is actually harder to return to its original owner than if it was fiat. There's very little ways to prove you own that Bitcoin once you've lost access to it, obviously by design.