If you have blocked off the pipe and blocked off the hole in the airbox that the pipe connected to then thats it.
I have never thought about it pumping against the blocked off pipe and now I can't get the thought out of my head, but I suppose the fumes would just go back into the engine and get burned off eventually.
Some owners must have been running their bikes for years with this mod done and I have never read anything about any potential problems that might occur.