If the situation with his dying mother is true, then you know what? My heart does go out to the dude. But Fox was right to fire him. Disappearing off your set should never be tolerated... especially if you're the director?!
The fact is they put up with Singer's behavior before. Many times. Heard stories of money (not per diem pocket change - major dough) disappearing out of thin air during the Superman Returns shoot and how Warner Brothers' accounting department couldn't make heads or tails over it. Such an extreme situation that when the studio signed Singer to another expensive "Pay or Play" deal on the Superman sequel (which instead resulted in Jack the Giant Killer), part of the stipulation was to shoot closer to Burbank... so they could keep an eye on the money. But such a situation isn't exclusive to him - happens frequently.
Something doesn't smell right, and it's not to do with "Maybe... maybe not..." allegations on the horizon. I think it has more to do with Fox wanting to look competent and in charge... in lieu of a major buyout from Disney, a company that notoriously doesn't take crap from any one filmmaker. Mess with the Mouse and you will be replaced in an instant and the film in question will still make billions. Not doing anything and letting "Same ol, same ol" continue makes Fox look bad as they are closing out this deal. Suddenly Singer's being MIA from the set (which everyone here agrees is beyond egregious) and having it out with his cast is unacceptable. When it usually was... because Singer made them a lot of money.
But a Disney buyout (rightfully) outweighs Singer's internal stock with the studio. Hence suddenly these stories get out, when they never did before. Just some food for thought.