What would happen? They would have no indication of it being what worked for them, unlike What happens if you answered a question, questioner says thanks, but didn't accept your answer as correct?.
What would happen?
It just waits there waiting for its owner to return.
It keeps getting bounced up the feed by the community user, at regular intervals for any more helpful answers. Post regarding the details regarding question bumping
The problem with such questions is that; even though there are multiple answers underneath it, we can never know whether it helped the OP or not.
From personal experience, commenting underneath the question like this helps:
Did one of the answers here help you? If yes, then maybe you'd want to accept one of them.