The Russian and Chinese vetoes of the Security Council Resolution on Syria and the closing of the US Embassy in Damascus are further reminders that, more than any other "Arab Spring" case, Syria's agony is caught up in the complex geopolitics of the region. Like the Lebanese civil war a generation ago, the Syrian conflict is exacerbated, and perhaps fueled and funded on both sides, by regional players. With growing signs that the new Egypt will be estranged from, if it does not entirely abandon, its traditional strategic alignment with the US (and less overtly, Israel), some no doubt see Syria as a way to rectify the balance; lose one from "our" camp, win one from "theirs." That's bipolar, Cold War kind of thinking, but it's true that Syria's role as Iran's one Arab ally, and as the bridge through which Iran supplies Hizbullah in Lebanon, means the outcome of the struggle has implications far beyond the boundaries of Syria. As was the case in Lebanon during the war years, that is not good news for the ordinary people on either side of the struggle, since it tends to prolong the conflict. Unlike Libya, where Qadhafi had few friend left near the end (well, okay, Burkina Faso, but they're no match for NATO), Iran and arguably Russia have an investment to protect in Syria, while the West sees a chance to alter the balance.
I am not an advocate of Western intervention in Syria, not from any lack of horror at the humanitarian toll if the conflict continues, but due to the lack of practicality as well as the danger of escalation. In Libya, where most of the population and economic resources were on the Mediterranean, with NATO airbases in Sicily, southern Italy and Cyprus and French and Italian aircraft carriers in the Med, the logistics were easy. In Syria,where the major cities are inland, one would have to operate from eastern Turkey or enter from the sea via the Latakia corridor, or else overfly Lebanese airspace. Logistically it would be a problem, and while Turkey is actively working against the Asad regime, use of Turkish bases would further complicate the geopolitical tangle.
For all the Western outrage about the vetoes, Russia and China are no doubt acting in what they perceive to be their own interests, or those of their client. (Bear in mind that the overwhelming majority of US vetoes in the Security Council have been on resolutions involving Israel.)
The Syrian tragedy will go on, UN resolution or no, until something changes either the balance on the ground (where there are signs of gradual strengthening of the rebels) or a transformation of the geopolitical mosaic. An Israeli attack on Iran could make the Syrian civil war (or whatever you choose to call it) part of a much larger regional struggle, in which anything could happen.