Yes, I think Fatah is strong enough in the West Bank, but it would be disasterous if Hamas and Fatah repeat the violence there. Hamas are more powerful in Gaza than Fatah is strong in the West Bank regarding the support of the respective populations. The West Bank is much bigger and more spread out compared to the small and densely populated Gaza and Hamas could possibly neutralise the strenght difference. They also did well in the elections in a number of West Bank cities, demonstrating that despite the lack of a sizable military force in the West Bank, they do have some public support there. But I think that they will do everything in their powers to prevent this scenario. Hopefully Gaza is a show of strength and will be enough for Hamas, at least for now.

There have already been reports that Fatah leaders are asking Israel for help in facilitating their exit from Gaza. I dont know what the response has been.

It seems that (depending on how quickly the violence in Gaza is reduced) that there is a high probability that the Fatah leadership will largely leave Gaza. I suppose they may be able to come to some sort of agreement for the sake of "unity", however as this is a myth, im not sure that they will be capable of this. Could happen though but it would be only a token gesture. Hamas and Fatah know who controls Gaza.

Fatah wont leave the West Bank unless they are forced out. Hamas dont have much military power there and thats whats important in the short term.

Its been reported that both sides have executed prisoners. Fatah have already begun taking actions in the West Bank - at least 36 Hamas people have been taken into custody in the last few hours.