If the solenoid failed in the closed position then I don't imagine there will be any problem (I'm not sure if the injector pulsewidth is reduced to compensate for fuel vapour) until the canister cannot hold any more vapour. I guess once the canister is full then you'll get a smell of petrol from the tank or canister.

If the solenoid failed in the open position then the fuel vapour will constantly be venting into the inlet manifold and the short term fuel trims will recognise a rich condition and lean off the desired AF ratio to suit.