And when I say market, I don't mean the supply side, I mean the demand. The sales figures show this. People are going to spend much more 4e stuff then they will OGL stuff. That is why there are going to be many 3 party publishers that will sign the GSL or at least go the no copyright infringement route. There won't be any lack of product supply.
Maybe not. Erik Mona over at Paizo has stated that subscriptions for PATHFINDER have increased weekly since the announcement of 4e and are currently at an all time high.
Market for OGL stuff just as much, if not more than 4e.
Your assertion is still up in the air. Folks in 3rd party may not sign, despite the 4e market, but because they ultimately lose control of their porduct, its on teh whim of WOTC.