I went to take some coons off of my stretchers today and they were all soft from the humidity. Temps here today got up to 70 and then we got a ton of rain. Needless to say the humidity went up. All the coons are not soft and won't stand out straight like a board. They would 2 days ago, so I know that they've been on the stretchers long enough. Do I need to leave them on the stretchers longer? Will they dry back out? Am I screwed?

Personnally, I would put them back on the stretchers and place a fan on them until things settle down again.

If your coons has been drting several days and the head , ears and tail are dry, don't worry about the hides. They will stiffen up as soon as it cools off.
I just finished taking about 400 off stretchers and they were pretty limp. A few days ago some of the same batch was stiff as boards, like to never got them off the boards./ Now they slide off the boards like they had grease under them.
If the skins are not completely dry they will wrinkle, if they were dry, they should be ok. They may curl a bit and if they do , just put a piece of cardboard on them and add a little weight.

Our damp humid climate I always kept a small heater going and a fan on everything, if not it takes forever to get anything dry and stiff here. Plus the mold and mildew starts to show up on leather if moisture is allowed to stay in the 'shed'.