If the Steelers win against Jax (or Baltimore) they are in the playoffs. At 10-6, they win the divsion unless Cleve wins out If Cleve wins out they eliminate Buffalo as far as the Steelers are concerned. A win vs a conf opponent give them 8 Conference wins, Tennessee can't have more than 7. Steelers get a Wildcard at least.
If the Steelers win vs StL and finish 10-6. They will be 7-5 in the AFC. Again, they win the divsion unless Cleve wins out (where again the eliminate Buffalo). The only way the Steelers miss the playoffs is if Tennessee wins the tiebreaker with them by winning out and finishing 10-6. But it will come down to Strength of Victory which could still go the Steelers way.
One win and the Steelers are almost certainly in the playoffs.