Guns can be re-heat treated successfully as is done with Mauser M98s . You have to know what you're doing.
If you know the type of plastic you can get an idea of what temperatures have been reached.
But the best way is to check the springs .If they are soft that's a bad sign. Does the steel have black scale formed on the surface ? If so scrap the gun !!Even if you could repair the gun it may be that the cost would not be worth it .If not done properly it might be an accident waiting to happen.
And Watson , bring your revolver !