The only thing Israel needs to worry about is the American money. No, not the money to Israel, but the money to Egypt. As long as the money continues to flow into Egypt, and is large enough for the military to continue to siphon off their cut, the country will be stable. If, and when that ends, they will be "outa there" in a millisecond, and with them stability. Israel might even consider sending a part of their 3 billion to help out. Cheaper than a war.
Aden hotel used by Yemen goverment hit by grenade (Reuters)
from the article: Why was Israel clueless about Cairo?