Humble Bundle CD-Keys

Keys will work forever, just save them in some file out of HB order

I think you mean the current Drift promotion. In that case, no, the keys usually expire within a week after the promotion ends.

Nobody can say for sure. It will, it won't. It's up to Humble or publisher's whim.

Bought keys do not expire.
Free keys/games do expire. I believe humble bundle tells you when it ends when you get the email.