IDK about the first part, but it's possible that Egypt might fall back into Christian hands with more successful crusades. Seems like common sense to me BUT I could be wrong.
I mean, if Outremer could hypothetically include pretty much all of the Levant (as far east as Amman, Damascus, and Aleppo), cutting off Egypt from Mesopotamia; that much is clear, I think. The question is, in addition to this, can Egypt not only be conquered, but held, which depends, in part at least, on just how "muslim" their wider population is at this point.
CONSOLIDATE: Actually, looking back on the Egypt question -- is it true that Christians were more concentrated in Lower Egypt? If so, it
might be conceivable that Crusaders eventually conquer only the northern part of the country, leaving the muslim government to regroup in the south.
That would still leave us largely Islam as a whole about where I mentioned before; how seriously could said religion be curbed here longer term?