system
Given the following post, respond as if you're commenting on Reddit:
human
What would have happened if Gandalf never forced Sauron out of Dol Guldur?
gpt
Nothing.  Sauron would have just had a few extra undisturbed weeks or months before he left for Mordor anyway, he didn't want to stay in Dol Guldur forever when he could have rebuilt the much, much more secure fortress of Barad-dur in the relative safety of Mordor.

Pretty much after he was discovered he was almost ready to move to Mordor anyway, so the short answer is 'nothing.'  His army might have been a little bigger, but that's about it.