I did a little digging and found this passage:
Teams that negotiate guarantees for players also negotiate scenarios in which the guarantees will void. Though these vary team by team there are some pretty standard void mechanisms that are used across the board. Such mechanisms include non football injury caused by performing dangerous activities such as sky diving, suspensions for personal conduct, steroid, drugs, or conduct detrimental to the team, incarceration, holding out, retirement, and doing something to undermine the team. As you go team by team you will see some different things that are team specific like failing a physical.
So it certainly seems feasible that Pittsburgh could get rid of AB all together and not suffer any cap consequences... if they wanted to go that route.