Here's the situation I ran into:

I posted an answer to Maximum $C$ such that every shape in $\Bbb R^2$ with area $<C$ can be placed to avoid $\Bbb Z^2$ and it garnered a few upvotes before I realized that it was utterly wrong and not really salvageable (the nature of the problem is to give a shape, and the shape I gave was invalid).

I deleted it, and came up with a new answer. The new answer followed basically the same proof idea as the old answer, but was for quite a different shape. At this point I didn't know if it was appropriate for me to add a new answer, or to (significantly) edit my previous answer and undelete it. I ended up doing the latter.

It wouldn't matter much except that there were already votes on the wrong answer, which would be invalidated by leaving the answer deleted (and I don't know if the votes should be invalidated or not). If the votes had been down votes, then it would make sense to post a new answer because presumably the down votes would be in response to incorrectness which would not (necessarily) apply to the new result.