[smokingrobot]

i dont know, maybe this is improper, but in this single situation, i'd say if you 3-bet and are just called, river brings a king and he bets out again, its the same as being rereraised allin on the turn, so you'd fold.

In response to EMc though:

If you c/c, what if he's allin on the river? Or say he just bets the pot?

You're basically in the same situation as if you 3-bet and he either
A) checks to you so you can gladly check it down and take the pot
B) re-re-raises, or bets the pot on the river or some other large number.