I wonder if the contracts with Russia and Qatar have any get out clauses.
There is no such thing. But countries boycotting events such as World Cup, after confirming their presence will be severely punished, if the past instances are anything to go by. For example, they can be banned from the next two or three world cups and other regional FIFA tournaments, in addition to a very heavy financial penalty.
I think widespread corruption at fifa makes this situation a little bit different. I doubt countries will boycott it after Blatter's resignation but there will surely be a few countries like England complaining that they should have the world cup or it should be put back to another vote. They wont pull out though.