On one hand the whole point of extending early was up front protection ($$$) for Gronk in trade for a more team friendly deal for the Pats, long term. Did he give money back when he was hurt? No? I didn't think so.
Now, on the other hand, this is Gronk we're talking about. And aside from his importance on the field, you think you'd want to take care of him as the message sent to the locker room otherwise could cause serious issues moving forward.
You can't operate on principle alone, in a vacuum. And frankly, I'm not worried about Kraft's great great great grand kids college fund. I'm a little out of patience for the ol' douche bag. Cap space, I care about, but they can find a way to make it work for Gronk.