Even with all the "on the cheap" talk here, the Russians really don't have the ability to sustain themselves in any sort of "global" reach for prolongued periods. Observers have been saying for years that they are a regional power and it's likely they've finally realized it. Hence why the Syrian Mission was so limited.
Deploying any armed forces not within your own nation (unless specifically geared for it) is really bloody expensive which is why so few nations on earth are actually capable of it. The Russians have actually struggled when following their "bite and hold" strategy on neighboring states, let alone being able to push that to a nation on the other side of Turkey several thousand miles from home.
That being said, the main purpose of the Russian presence was to augment the Syrian airforce with fighter-bombers and to allow the Assad regime the local air superiority it actually needed.
There was little risk of Coalition-Russian clashes as the strategic aims of both overlapped enough for it not to matter thanks to everyone being opposed to Al-Nusra and ISIS.