Please consider the following hypothetical scenario: the SNP issue a legally-binding commitment that in the event of a Yes vote for Scottish independence, they will permanently disband the party and step down from government as soon as the independence negotiations are concluded. In that event, how do you think you would vote in an independence referendum?
Oh-kaaaaaay, Stu. I mean, why stop there? Why not ask people how they would vote in an independence referendum in the hypothetical scenario that Nicola Sturgeon and the entire SNP cabinet make a legally-binding commitment to blast off on a rocket bound for Saturn the following day? I'm not a lawyer, but I have my doubts as to whether it's even possible for the kind of pre-commitments Stuart is talking about to be legally-binding. For the SNP to disappear "permanently", I presume it would literally have to be prohibited by statute in much the same way that Germany has banned any form of Nazi party. As for government formation, that's a matter for the Scottish Parliament at any given moment in time - options can't be closed off months or years in advance.
So what the hell was the point of Stuart asking such a ludicrous question? Reading between the lines, it appears to have been a propaganda exercise, intended to establish that the SNP are a drag on support for independence. If so, it backfired totally, because the result is the opposite - support for independence actually decreases from 50% to 47% when people are asked to assume that the SNP will no longer be around. That really shouldn't have been such a surprise to Stuart, because a number of people have become independence supporters precisely because they've seen the SNP run a devolved administration with a high degree of competence, and expect more of the same with the full powers of independence. As soon as you take away even the possibility of a post-independence SNP government, the reassurance disappears and those people are left with a considerable amount of uncertainty about what independence would look like and whether it would be a success.
Having failed to get the result he wanted, Stuart naturally does his usual "heads I win, tails you lose" thing, and tries to spin the result so that it supposedly still shows that the SNP are the main obstacle to independence (because their voters allegedly care more about maintaining SNP rule than about achieving the party's goal). Yeah, whatever.
In science, there's an important concept called 'falsifiability'. One implication of it is that if you set up a study in the hope of proving that a theory is true, there has to be a way in which the study could also prove the theory is false. For example, if someone is claiming to have psychic powers, and you ask them ten questions to prove they are a charlatan, you have to accept that if they get all ten questions right, you've failed to prove what you set out to prove. You can't then shift the goalposts and say "oh, but this just proves how cunning a charlatan he is!"
Stuart's claim (that his poll proves that the SNP are the main obstacle to indy) fails the falsifiability test, and fails it utterly. He would literally have made exactly the same claim if he had got precisely the opposite result - and that was what he was seeking.