I wanna keep the numbers.
And I don't like the idea of filling gaps with newer works, because the numbers also makes it so that newer works are always on the highest numbers, which makes work for us easier because we can immediately see works that need summaries at the bottom of the list. (Speaking of which, there's still no summary for Ammy's fic, guess I'll have to do it myself after all).
If it's a work that's no more than, let's say, ten numbers away from the most recent one, then renumbering is okay.
But imagine what happens if someone decides to delete #4x ? Renumberig hell~
In such cases, I'd say we simply leave the numbers blank or put in a -Deleted by author- notice in its stead.