Based on what we've seen from Harvin on the field, the Vikings might want to see what they can do to make him happy and avoid such a move.
The folks over at Pro Football Focus, who tirelessly research the NFL more than almost anyone else in the world, have Harvin rated as the 6th best WR in football, and it's clear that his impact in the return game is nearly unparalleled.
If a team wanted to pry Harvin away from the Vikings, they'd probably have to give up a 2nd round pick as well as perhaps a 5th or 6th, and that would net them one of the most dynamic slot receivers in the league.
Sam Monson of PFF even goes so far as to say that losing Harvin would be akin to the Vikings losing Randy Moss back in 2004:
I'm not sure if the Randy Moss comparison is completely valid, but there's still value there. If the Vikings lose Harvin, they'll have to rebuild their receiving corps once again from the ground up, while still trying to develop young QB Christian Ponder.
That certainly wouldn't be doing Ponder any favors, and would also make it a lot easier for defenses to key in on Adrian Peterson.
The Vikings need to find a way to throw some more money at Harvin in the form of a long-term deal, and see if they can't make him happy in Minnesota. Otherwise, they might be looking at a lengthening rebuilding process that has already been years in the making.