I'd be worried about a soft tissue injury. Even if that doesn't happen it'll take a few weeks to catch up to form if he does at all this year. Chris Johnson last year after the holdout would be an example of why I'd be concerned. He never caught up and had an off year.
I have to say no. In a PPR Gronk is gold. That and MJD didn't get paid and missed all of camp. I'd say keep the solid starter. MJD is too much of a question mark. This is coming from someone who hates that RB core mind you.
I would take a look at the first couple of games before I make that trade. Too much risk involved right now, missed whole training camp, pissed at the owner, team still blows, doesn't know the playbook. See how he looks after game 3, then make a decision.