Well the We love closing party looks like it is on on September 30th.. and DC10 is still open on the Monday...but I'd heard that may not be correct.
Ibiza , I'm assuming, will still be lovely at this time of year, but if you are planning on a clubbing holiday, you should have gone a little sooner, to catch all the closing parties.
Check out the clubbing guide /calendar on this website
Not trying to make you feel worse,

, but if you are going for a primarily a clubbing holiday, why wouldn't you research this before you went?
Its kind of like booking a ski holiday in July and wondering why there isn't any snow.
Sorry !! I just had to say it!
If you are just going to see the beautiful Ibiza, then I'm positive you will still have a good time!