Firstly, the way in which the United Kingdom was formed is of zero relevance to the formation and constitution of the UK in 2016. Just as, for example, the Republic of Italy is a single nation state in 2016, regardless of the fact that there were at one point fully-independent city-states in Italy. In 2016, Venice (for example) is nothing more or less than a city within the Republic of Italy.
Again, are you stating opinion or claiming fact? The way that a Union is formed is of course highly relevant to whether that Union can be dissolved unless that has been explicitly overruled by some other action. Legal minds disagree on a number of matters related to this so it's in no way as clear cut as you suggest.
Secondly, I'd go back once again to an analogy I used earlier of a business merger, since it's entirely relevant to the matter in hand. Remember that one company, A, merged with another company, B, in (say) 2005. The merger would have had to have been ratified at that time by the boards of both A and B before going ahead. Terms of the merger would have been agreed by both A and B at that time. Suppose that those terms included the fact that the HQ of the merged company would be based at the A factory, that A and B would both still maintain local management boards, and that B would be allowed to keep its own sports and social club separate.
But once the merger had been approved and ratified by both A and B (and respective shareholders), a single company would have been formed - The United AB Company. With a single executive board. And a single set of shareholders. And a single class of shares. And as I keep trying to point out (fruitlessly, as it turns out, in the face of interestingly blinkered opposition.....), if the management board and workers of the former B decided in 2016 that they now wanted to "demerge" from The United AB Company, they simply could not unilaterally go ahead and do so. They could put in a request to the executive board and shareholders of The United AB Company, but it should be as clear as day (that is, to anyone with any understanding of law and practice and a rational, objective mind) that a) the splitting off (or otherwise) of the B unit from The United AB Company would be a matter of direct relevance and importance to the executive board, shareholders and employees of The United AB Company, and b) only the executive board and shareholders of The United AB Company could ultimately decide whether or not the B unit would be allowed to split off from The United AB Company.
Yes, that's one way to look at it. Another way to look at it would be a marriage between two people. No-one would argue that a divorce can only happen if both parties are in agreement.
Or even to use your analogy if the board members and employees of company B decide they want to leave the company then they cannot be forced to stay.
And why I say the details of how the UK was formed matter is that, for example, the Scottish Parliament was never dissolved. Merely suspended. Ditto the English Parliament. Scotland has kept its own legal system, education system, health service, etc.
So you cannot really have it both ways. You cannot argue that the details and legal arrangements matter when it suits and then that practical de facto matters are important when they suit.
If you take the pragmatic approach, Scotland in 2016 is for practical intents and purposes a region of the UK in the eyes of the international community. Albeit a bit of a special case. But if you take this pragmatic approach then you also arrive at the conclusion that no UK government can realistically hold onto Scotland in perpetuity if the population expresses their democratic intent to leave.
If you want to look at it as a purely legal and administrative point of view then it becomes a battle of lawyers interpretations but I think eventually you would also run up against the basic principle that the Scottish government of 300 years ago can't commit the people of Scotland to a situation in perpetuity that they are unable to extract themselves from by some legal means.
To give another comparison, imagine that Article 50 wasn't included in the EU statutes and that people were claiming there was no way for the UK to withdraw from the EU without the permission of the EU. It would rightly be seen as scandalous arrogance and a complete over-reach of power by the EU.
If we are being honest the most likely path for this is that after protest Westminster agrees to a referendum and Scotland votes to stay in the UK. The matter would then rightly be dead for sometime.
Probably the best hope for an independent Scotland is for May and her right-wing goblins to try to thwart it. That might just well be enough to push a number of swithering Scots over the edge.
