So, 1.6 million people and 45% of the people who voted Yes? It's not as if this is a small band of rebels hiding away in a cave - it's a large portion of the Scottish population, who will only become more determined if the promises of further devolution aren't delivered. Not to mention that if those promises aren't delivered, many of the No voters who wouldn't mind an independent Scotland, but either felt the risks were too high or that we weren't able to go it alone at the moment, will soon become tired of the UK as well. Again, I'm not saying that we're going to be having another referendum next year or anything, but depending on what happens within the UK in regards to reform, it's an issue that will probably come up again at some point. Difficult to tell when right now though because we're still to see what changes will be made.
As for the rest of it, your assumption that Scotland completely depends on oil is the sort of stuff that the No campaign were banging on about for ages, despite it not being true. It's certainly a superb asset to have, and a massive bonus, but Scotland has plenty of resources and would've been able to stand on it's own feet economically. A redundant argument now since we voted not to do so, but we're unlikely to be a bunch of scroungers if this comes up again. It's accusation that we are which actually creates a lot of the discontent from Scots towards Westminster and the UK.
If we were to hypothetically struggle in the future post-oil though and depend on England, things could get messy. That would naturally result in cuts to our budget (unless the current way of doing devolved powers changes) which would only lead to more discontent and will to leave. If our budget wasn't cut, you'd probably see a lot of people in the UK wanting to cut as adrift. But, again, all hypothetical. We'll see what happens with the promises of powers which might not be promises after all. Following that, we'll get a better idea of whether this is likely to be a lifetime issue, or a generational one.