Johnson, along with Morrow and Lewis, is as close to being a "difference maker" in the passing game as anyone we've had under Mullen. We have some depth at TE, but he is unquestionably the best receiving TE on the roster. And in case you haven't noticed, we are going to throw the ball more than we have been.
With the exception of Morrow, we basically have an army of slot WRs. Johnson is the only other guy we have who can go up and get the ball, and he has shown a knack for getting open. We were counting on him to play a big role in the passing game this year, and now he may be lost for most of the season.
Green sucks, and Hill isn't as good as Johnson. Warren is still developing, and he is more of a traditional TE than a H-back/receiving threat.