The SNP would still have a very important role if they lost the independence vote. They'll probably be stronger than they would if they won as they have a good record in shielding the Scots from Westminster policy whereas the other parties are just by-blows of the main parties full of people who couldn't get chosen as a Westminster MP candidate. If they won the independence vote then I'd see Labour becoming more resurgent as an independent party and taking the country back into minority or coalition rule.
I think the "yes" campaign will build steam as time goes and it'll be a close-run thing but I think the "no" vote will win.
Currently the polls are pointing to a No vote, followed by the return of an SNP government, with the possibility of another majority. On word of warning, though, is that the polling organisations don't have a great track record in Scotland. One pollster has spent the last twelve months asking "how would you vote if the referendum was tomorrow?", reflecting their practice in voting intention polls, not seeming to understand that the referendum is not going to be tomorrow, it going to be on a certain date. When they switched to asking how they would vote on September 18th, 2014, the number of don't knows trebled from 10% to over 30%.
One thing to remember, and I don't know if this comes across south of the border, but the independence campaign hasn't really started yet. Yes Scotland have been building up a grassroots network of volunteers, which have been doing some kinds of things like running stalls in High Streets and at community events, and recruiting and training campaign volunteers. Other than that they have spent their time reacting and responding to almost daily scare stories in the press (some more ludicrous than others) and claims by Better Together and their supporters.
The SNP have been very quiet and, in fact, when Alex Salmond gave his speech the other day I realised I hadn't heard him discuss the independence issue for quite a while. Nicola Sturgeon, who is actually leading the government's case for a sovereign Scotland, has done a number of interviews and debates, but it has all been a bit low-key. I would expect things to pick up after the November white paper (26th?) and then in the new year. And the official campaigning period will be 16 weeks, as opposed to just over 3 weeks for a general election. This will be a time of prolonged and intense debate, so things could change
What happens in the event of a No vote is, of course, speculation, but it does offer up opportunities for both the SNP and Scotland. Whilst obviously a setback for a party dedicated to the re-establishment of an independent Scotland, it would also free them from that burden for a while. The question would have been asked and declined, but the party could then go all out to win the further powers and responsibilities that Scotland needs, and that a majority of people in Scotland support. Further autonomy within the UK has been hinted at by the British parties if we vote No, and this would be the time to pressure Westminster into delivering. I could see the SNP leading a successful and popular campaign on this which the others might find difficult to handle. How could they possibly argue against something like full financial autonomy and the granting of all powers other than, say, defence, foreign affairs and certain economic functions? If, as the unionists claim, Scotland is subsidised then the rest of the UK would stand to gain.
Westminster would refuse, of course, but that would kick off a whole new ball game.