Michele Dunne isn’t ruling it out:
What could easily happen is a return to the sort of low-level insurgency and domestic terrorism that plagued Egypt during the 1980s and especially the 1990s. That period saw the 1981 assassination of President Anwar Sadat, a 1995 unsuccessful attempt on Mubarak’s life, a 1997 attack in which 58 tourists and four Egyptians were killed in Luxor, and many other incidents in which jihadi Islamists targeted Christians, liberals, foreigners, and government officials. Tens of thousands of Islamists were imprisoned, often for lengthy periods without charge. The Sinai will probably become much more dangerous than it already has, further setting back efforts to restart tourism and get the economy on track. Clashes between Islamist demonstrators and security forces are likely to continue, and those between armed Islamist and secular gangs might become common.
Will the post-Morsi violence become an actual civil war? Several more shoes would have to drop—a return to arms of the so-called repentant former jihadis, the drift toward extremism of more Brotherhood members, the formation of more and larger armed Islamist units in lightly governed areas of Egypt, such as Sinai and the Western Desert—to bring about that unhappy prospect. But it can no longer be excluded altogether.
Earlier debate on the subject here.