Here's the thing. It's clear that the Pats want to run all of their plays with two TEs on the field. When you add Welker and Edelman into the mix, that makes four guys who are trying to do damage in the middle of the field. So my question is this: once AHern returns, what gives? I can only assume they'll return to where they were and I see no reason to think that Edelman just all of a sudden disappears. The result is going to be less snaps for Welker. Even further, I don't think the idea of them trading Welker away is out of the question, which would likely be disastrous to his production (unless he went to the Packers, Saints, or Giants maybe).
My suggestion is that if you own him, hold on tight -- his value is low now and with AHern out, he's likely to rebound by default. As soon as he has a week or two of production, start shopping him for full value. If you don't own him, it's a tougher question, because it will really depend on the discount you're getting. I wouldn't pay anywhere close to full price for him now though.