I see two possibilities:
1: They try to keep up the energy kick and scream bloody murder at every turn, but never achieve anything, as they have exactly zero leverage to affect anything in Westminster. They fizzle out, and nothing much happens and things return to normal. Their big shot, independence referendum, has been fired and can't credibly be reloaded and re-fired anytime soon. Even Nicola Sturgeon admits this.
2: They get down to business and negotiates as a serious counterpart for actual regional political influence. This means getting their hands dirty on actual politics and compromise and at least toning down the Tory-hate-rhetorics, which could prove a very bitter pill to swallow for their base. See: Liberal Democrats, 2010-2015.
Apologies if you already knew that, but there's a lot of commentary about recently that seems utterly ignorant of those facts.
It's probably worth reflecting on your words here too: "never achieve anything, as they have exactly zero leverage to affect anything in Westminster". That's a double edged sword for people who want to keep the union together for the benefit of all.
Unionists leaders would certainly do well to make sure the Scots feel part of the union - but with a SNP in scenario one, Westminster is unlikely to be the venue for that.
They could work directly with Holyrood on efforts, or work directly through non-devolved powers.
That's fairly aggressive.
Meanwhile the SNP where working together with the Tories in the devolved parliment to get things done (despite popular lore, there are actually Conservatives in Scotland and with PR they get a proportionate number of votes in the running of the parliament).
Clinton, who else?
Pessimistically, it means an acrimonious break-up of the UK to the detriment of both sides, though that depends as much on what the Conservatives have planned as what the SNP wants and is able to do.