How does Wheatley recover after GLaDOS's crush?

It doesn't. You'll notice that since then, Wheatley's eye appears cracked. Take a gander.

When you first see him after he is crushed he rambles on about something while you jump up and down to hear it. I always assumed that the game developers intended to give you the impression he was telling you how, but he didn't realize you couldn't hear him between jumps. I think they did it this way to develop his character as someone who was incompetent.

What's interesting is that in "The Final Hours" they reveal that for the longest time they were going to have Wheatly die off when GLaDOS awakens, it's only in the last year of development that it was decided that the character should live and take on a larger role in the game.

While Wheatley obviously sustains some damage from GLaDOS's rough handling, he's not actually offline when she discards him and tosses you into the incinerator. As Wheatley's line in this video suggests ("There I was, just lying there, you thought I was done for, but—"), he's just playing dead.