"by removing the one person able to hold it together."
er, do you mean Bashar Al-Assad by any chance? The man who faced a peaceful rebellion in his own country and ... now look at it (!!)
The fact is that Russia is not "joining up" with Assad. It is merely bolstering its military and diplomatic support for his campaign of genocide. And all because he is their only friend left in the region.
The question is a bit of a no-brainer, because it isn't as if helping Assad would serve the interests of "the west". All it would do is make a terrible conflict much, much worse. Assad is not in control of his country, to put it mildly, and the amount of military effort that would be needed to put him in the ascendant, never mind put him back in power, would be so great that it would escalate the conflict dramatically, boosting the numbers of refugees fleeing towards Europe in the process.
Put it this way: a coalition of responsible nations came together to remove Gaddafi (effectively) but that didn't turn out very well did it?
So what are the chances of an alliance with another war criminal in a far worse conflict turning out for the best ...