Hines raises an interesting point, and yes, the Steelers have to make a move at TE when Green is activated.
1. Jessie James - He is starter capable and will not lose his roster spot. Even when Green comes back, I can see JJ continue to start while working Green in with subpackages. I say this with confidence since JJ is receiving close to the same snap counts that Heath used to get. Also JJ may be the better blocker between he and Green.
2. Grimble - probably #2 on the depth chart as we stand today. And looks to be the most explosive pass catcher of these 3. Not as confident of a blocker, but not terrible at it either.
3. Johnson - I think initially, he was going to go. Then he played this year, and wow has his blocking improved. Improved to the point where he is our best blocking TE. He is position flexible, offering help at FB or TE, and is also a capable pass catching threat as well.
It's going to come down to Grimble and Johnson. If Nix isn't 100%, you can't cut Johnson yet, since the team will need a fullback. If the team wants more versatility in the passing game, they will keep Grimble over Johnson. I think Grimble is the only player who will be PS eligible, so that will also be a factor, but with what he has shown, will he clear waivers to get there?