By this point, the Republic was doomed. The Optimate was already losing power, both from demographic reasons and the fact they murder Caesar has not done them any good. Even if they win at Philippi, I doubter the rest of the Roman world would weclome them.
Wait another generation for the next big war, the next skill military commander that win major victories, a strongman who is able to carry out major reforms and you have your Empire and Emperor. Noting can stop the next generation of powerful governors and generals using their popularity with the legions to march on Rome and seize power. Sulla did it, Caesar did it, Mark Antony and Octavian did it. There is nothing to stop whoever comes next, and that person can and would likely turn the Roman Republic into the Roman Empire.
Egypt will also survive for the time being as client state. (In part of how the Republic preferred to govern much of their Asian holdings-indirectly, in part the Romans would face a lot of resistance, and in part whoever conquers Egypt will be the richest man in Rome, and no where wants anyone that powerful.)
The Empire is coming, you can't stop it.