It is a big blow to lose Crabtree but it isn't the end of the world.  The 9ers aren't WR driven and they were winning last year without Crabtree catching a lot of passes from Smith.  I think that one of the kids will step up and the one who I think may do a lot of damage is Lockette. He seems to have the combination of speed, size and hey, he was with Seattle so why not...

I also wouldn't be surprised to see 4 WR sets.  Without Crabtree, this could actually help the offense.  Going back to BWO where the passing game opens up the running game.  I think the 9ers will be more than fine until he is ready to get back.  Actually, it may light a hot fire under him during rehab while the offense is running on all cylinders.