The thing is, if they beat the Cardinals and Tua looks decent, they are still right in the mix for a playoff spot if he can stay healthy. Wild card slots 6 & 7 are going to be in competition for by the Bengals, Colts, Broncos, Chargers...and Miami could be in that mix if they get going.
If they lose to Arizona, I'm not even sure it's a smart move to play Tua at Buffalo. He has gotten injured vs the Bills a couple times now. That's a scary game for them.