I agree Mihailovich was screwed.
But the big problem he had was not so much diplomatic duplicity, though that no doubt existed, it was geography.
There was just no way the western Allies were going to get massive troops into Yugoslavia in time to prevent it being occupied by the Red Army, which is the only thing that would have prevented a commie takeover. The US and UK, understandably, had more important things on their minds in 44 and 45 than the post-war fate of Yugo.
As you say, Greece and Austria were just barely kept out of Stalin’s clutches. It is unlikely a similar effort in Yugoslavia could have succeeded.
So while Mihailovich was abandoned in a rather shameful way, it’s not likely his fate would have been much different if the Allies had stuck by him to the end.
It's possible that the Western Allies could have gotten troops into Yugoslavia.
In the late summer of 1944, they came close to breaking through at Bologna on the Italian front, which would have gotten Allies out of the mountains and into the Po Valley. Had they made it through the Ljubljana Gap, a relatively flat area between the mountains in western Slovenia, there was mostly flat and rolling territory between there and the Black Sea.
Churchill wanted to push for the Ljubljana Gap but was opposed by senior American officials.