Is there an etiquette for how to deal with (your own) answers in questions that later get identified as duplicates? For example, I answered Convert String 'ten' to Integer 10, which someone noted in a comment as a duplicate. Then I noticed several other answers were deleted after that comment appeared. Am I expected to delete my answer too? While my answer is simplistic, it doesn't appear on the "original" question. Should I add it there?
First, check the target post to see if there are any answers that cover your own answer.
If the information in your answer isn't in the other question, keep it. As a really good point, consider flagging the questions to be merged. This consolidates all of the data into one question instead of splitting it between two, and you retain all of the event history that occurred on the original answer.
If the information in your answer is in the other question, then it's up to you. People can try to accuse you of gaming for reputation, but even the most eagle-eyed of dupe hunters have missed things. Some people suggest Community Wiki'ing your answer as to stop reputation gain, others suggest deleting your answer and supplementing an existing one with comments, while others just say leave it.
Honesty beats out protocol any day, so if you don't feel guilt in an honestly provided answer then I don't see why you should listen to anyone who tries to fault you for leaving it up. In my opinion, it's no more damaging than how 5 users can provide effectively identical answers to the same question simply because they didn't know anyone else was posting.