I wouldn't lose any sleep if Assad ended up hanging from a street light. But that's not my decision, or yours, unless you are Syrian. Although these things are hard to measure during a war, it appears people in Syria aren't really looking for that. Most people live under government control and have taken it to be the least worst option. That's hardly an endorsement for life under Assad, but it is a recognition that people believe the opposition, at this point pretty well exclusively jihadists, would be worse. It's not difficult to see why, as these same people are setting up slave markets in Libya, a country that quickly went to hell after they lost their despot because of an American regime change project. This is hard for us soft first worlders to comprehend, as we've never had to make such an unclean choice. It doesn't sit well and our moralism demands we pick a side.
We usually only hear about the regime and the opposition. But if we must choose a side, you'd have to sympathize with the Syrian Democratic Forces, a coalition of Kurdish leftists and Sunni Arabs who control a part of northern Syria, if you had any shred of humanity. That's not meant to be an exaggeration. These people, and it's important not to say "guys" here because they have a impressive contingent of Kurdish female fighters, are the only force that hasn't committed a massacre. They are the only force that isn't completely authoritarian or rabidly sectarian and reactionary. They also are good fighters, both the Americans and Russians consider them impressive. This is all fairly amazing given the context, and makes them a pretty easy choice.
The SDF is not a unifying force, however. They don't claim to be, and likely have no desire to be. The introduction of Sunni Arabs was a marriage of convenience and it's surprising it has lasted this long. They have a sort of strategic indifference to Assad's army right now, although they have battled in the past. They are absolute enemies to both Islamic State and Turkey, and (somewhat) allied to both Russia and the United States, which is quite impressive (and says a lot about how disgusting The Turkish regime is).
If the United States decides to oust Assad, the most organized groups within the opposition will take power in Damascus. This means the jihadists. This also means another civil war, certainly between the jihadists and the Kurds, but also between rival factions within the jihadists (e.g., Libya, Afghanistan). This also could very well bring Turkey back into Syria, as they are not one to miss an opportunity to attack weakened Kurds on their border. If the United States doesn't pursue regime change, and Assad is able to solidify power, there is a greater chance of some sort of agreement for Kurdish autonomy in the north. While this is no certain road to peace, Turkey would surely consider this a disaster and fighting could break out between different Kurdish groups and/or between Assad and the Kurds, it's also the best worst option.
Many in Syria understand this, which is why they aren't nearly as caught up in arguments over Assad's character as silly American pundits and much of the human rights industry. It's tough for us not to play hero, but history shows dead bodies pile up the fastest when we start thinking all these complex and murky choices are always ours to make.