In my opinion the accepted answer should permanently stick as only the original question submitter has the ability to accept.
No, the answer acceptance stays. Here's an example of a question from a deleted user with an accepted answer.
The author of that answer retained the earned reputation. (As a moderator I can see when the user account was deleted, so I checked reputation events on both that day and the day the answer was accepted. The deletion didn't affect the answerer's reputation.) Based on a suggestion from CrazyIvan in a comment, I checked the Community user and found the acceptance event there.
One exception: if the deleted account was ever involved in voting fraud, all votes are removed regardless of recipient (source).