I had already cleared out Greenspring Hollow. I don't get the dialogue option to drop the quest and Aela won't let me take another quest. What do I do? It's been MONTHS in game since I cleared it out so obviously it doesn't respawn.

I had this exact same problem. If you are on PC, try this:

Setstage CR02 20

Also, a note about respawns...
You say it's been months but have you avoided this area completely in that time? The respawn timer actually resets to 0 every time you reenter a cell. Thus, if you were to keep checking for that bear every 9 days, he will never show up.

Thank you for your reply. Sadly, I am on PS3. Concerning the respawn timer though, I will try that, though I'm fairly sure I had gone at least 10 days in game without getting close to that area. But I will try again and see what happens.