How to recover vegetables that get "refrigerator crisper chill"?
I'm sorry to say this, but I think prevention is the best answer. Once you're vegetables freeze things happen at the cellular level that changes the nature of the vegetables. For example, ice crystals pierce cell walls which destroys some of the structure, which is responsible for the crispness and crunch of the vegetable. I don't think there is really a way to "fix" this, once it happens.

That said, cooking does something similar to vegetables. Cooking destroys cell walls, which is why cooked carrots are so much softer than raw carrots. I would think that vegetables that stand up to cooking would survive freezing the best (such as your mushrooms). On the other hand, somthing like lettuce is a lost cause, once frozen.