Georgia could have been more successful if it was less busy destroying russian peasekeeping forces and shelling Tshinval and actually think about possible russian retaliation.
Yes. Roki Tunnel is the only lifeline linking S. Ossetia to Russia, nasty road through mountain pass being abandoned after Tunnel's completion in mid-1990s and largely impassable for vehicular traffic. What's more important, mountains are too high to be overflown by loaded helicopters and there's no landing strip in N. Ossetia suitable for heavy transport planes. Severing the tunnel would essentially destroy Russian ability to fight land war in the region and, as we know from Yugoslavian example, air power could only do so much against determined land force. Russians would have to conduct it's bombing campaign against backdrop of unbelievably hostile public opinion, which would have seizures over each real or invented Russian crime (if there ever be shortage of real ones, wich term "crime" interpreted as "each bomb falling on Georgia"). This environment would make sustained bombing campaign suicidal for Russian leadership and Russia would have to pull out.
On more general note, there're preciously few land links between Russia and Georgia (one more to be exact) which could sustain any logistical load worth talking about. So, if assault through Abkhaz territory or landing on Georgian shore is possible, land invasion is very tricky.
There would be much disappointment in Russia and further loss of prestige internationally (but probably less harsh reaction, maybe even "let's pretend that nothing happened").
Very likely. Attacking Russian peacekeepers and indiscriminate firing of Katyusha rockets at their protectees is not the stuff world media are willing to notice.
Georgia gets free hands in Abhasia too. Abhasia may lose any faith in Russian help and become willing to accept Georgian terms without fight (but again it may not).
I would not be betting on Abkhazia's losing heart here. It is very different case. S. Ossetia, with it's tiny population, crazy borders (those guys went to a great pain to exclude most of Georgian-populated villages from the territory they lay claim on) and underdeveloped infrastructure, can notsurvive without Russian protection. Abkhazia, on the flip side, won it's independence with nothing more than very limited arms supplies from Russia (Georgia inherited infinitely more equipment from the Soviet Army). They have defensible borders, rail and sea link to Russia, and mountains are much lower here, so war against them can not be won by a single brazen attack the way war against S. Ossetia can.
With the ongoing civilian traffic, Georgia could not risk collapsing that tunnel.
Collapsing the tunnel would be almost impossible without establishing control over it first, and, if you control it, why demolish? However, I don't think that fears over civilian deaths were very high among Georgian leadership, who started the war with Grad attack of sleeping civilian neighborhoods in the middle of the night.
