So if he has the sense that they're not liable to be picked up past the next season, then the smart move is indeed to only sign a one season contract so he has a parachute if and when the cancellation hits.
Also, if they don't get cancelled and the production company really, really wants him to stay on, they can renegotiate down the road (probably for even more money and/or less time.) And since his schedule would have been freed up, said negotiation would have to take place around any other commitments he's made, instead of the other way around. So either way, he'd be covered.