If you delete your own question, the reputation change from that question is reversed. If someone else changes their best answer away from your answer, you lose the
+15 reputation from it.
Stackoverflow has, with a couple exceptions here and there, a rolling reputation calculation. Reputation is added and subtracted from your total as you accumulate it, and as such, if you delete a question, your reputation gain/loss is reverted.
See also: How does "Reputation" work?
one of your accepted answers loses accepted status: −15