Just one comment related to the role of economic factors in Hamas' retaining power. It is of course quite possible that Hamas would try to put an end to further elections, but that would fail unless it either greatly weakens Fatah or they shared power. Still, my post and Posner's emphasize that one election is not democracy, and time will tell whether free elections will continue.
The Palestinian people being ruled by Hamas are very poor with rampant unemployment and with out migration of the most talented. Hamas could possibly replace the one and half billion dollars or so received in aid from other Arab nations, Europe, and the US. Venezuela and Iran alone could give that much, and rich Saudis might also continue to provide generous assistance.
But even twice that amount would not be enough to generate any significant economic improvement in the lot of the typical Palestinian family. The government has to encourage or allow sustained economic progress to accomplish that. I do not see how that is possible, nor are there any historical examples in modern times where that has occurred, without investing in and retaining productive human capital, and encouraging trade in goods and physical capital with other nations.
Can Hamas achieve that while maintaining the destruction of Israel as its primary goal? I think not. So Hamas can highlight its opposition to the existence of Israel, or it can push that into the background, and try to promote economic progress of the Palestinian people. I am not sure which path they will choose, but I believe the probability that they will elect to promote economic progress is being greatly underestimated.