If Assad takes back over Syria, it does not sound that crazy. If Obama had stayed out of meddling with Syria, Assad would still be running a stable nation. Obama messed that up.
The Kurds are making peace with Assad, and Turkey looks like it wants to make peace with Assad, as well. This will result in some degree of peace between the Kurds and Turkey, but the Kurds will always be tempted to plant bombs, it's their nature, and Turkey will want to reply, but they'll have to do it through a buffer zone.
The US aiding the Kurds (not as allies, because allies have a two-way relationship) only facilitated violence by discouraging the Kurds from being peaceful. The US presence was also preventing Syria and Turkey from negotiating a peace.
In the end, Assad will consolidate his power. And, everyone killed, maimed, or driven out of Syria will have been for nothing, if the US actually had a reason (to remove Assad) to be there in the first place. Sort of like the Iraq war didn't destroy WMDS, but the dogs of war have no regrets because "disarming" Saddam was never their real motivation (nor was compassion for Iraqis).
Obama was a very pro-war president. Hillary Clinton was also very pro-war. Trump is anti-war. This is why many neocon Republicans were #NeverTrump. They wanted Hillary to win, even if would let Hillary replace two conservative judges on the Supreme Court with liberals (giving the anti-Constitution wing absolute power, traitors).