Oh, sorry I misunderstood! Your steem monsters cards are in no way tied to your posting key. We never get or store your private keys in any way. They are associated only with your steem account name so as long as you log in with whatever is the currently valid posting key on your account all of your cards will still be there!
As for the account recovery mechanism, I don't have a link off hand, but I would just try googling it and I bet you can find some good info. Might also be some good info in the whitepaper.
For reference, I found a post from someguy123, I still need to read it ! :)
https://steemit.com/steem/@someguy123/how-the-steem-account-recovery-works-and-why-your-trustee-can-t-steal-your-account
Thank you !