They will NOT uncurl on their own. You will need to press them. However, make sure you are back in a low-humidity environment before you press them. Otherwise, the stamps will end up sticking to whatever you used to press them!
Also, don't wait to long. If you allow the gum to dry out too long (e.g., several months) you do run the risk of producing crackled gum when you do press them out.
For those of you who collect US stamps, this was one of the reasons gum breakers were used on US stamps in the mid-1900s.

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