much

They stopped Hezbollah from entering Syria, thus speeding up the crumble, but it was clear that without Russian air support the government falling was only a matter of time.

If you were to check out the changes on ground from 2012 to 2014 you'd see that Iranian intervention didn't change much, but right after 2015 (Beginning of Russian intervention) the revolution actually starts losing ground and fragmenting. Even the late Daraa insurgencies, where the government needed ground troops (The whole purpose of Iran's existence in Syria) was handled by Russian troops. LOL

So, yeah: Hezbollah by itself may have delayed the Homs takeover, but I can't think of many things that would've changed (maybe another massacre or two, but then what?)

Also, Israel just waited until the rebels took over and then magically knew where each piece of heavy military equipment was located and destroyed it all within like three weeks...