The British empire has told 65 countries the same things that you have highlighted and yet those 65 Countries still went their own way. As far as I am aware not one of the 65 Countries that gained their freedom have asked to rejoin and some have done rather well. I refer of course to the USA,Canada, Australia, New Zealand and of course Ireland. No one would infer in any way that Scotlands future as an Independent state wouldnt contain considerable challenges but I have no doubt they would be up to the task.
The fact is that if Scotland had been free to make their own choices when they had the oil bonanza then they might have been in the same position as Norway rather than as a poor region of the UK.
So I wouldnt be too pessimistic about Scotlands future if they chose to go it alone as I have immense confidence in their abilities to survive without subsidies designed to keep them dependent.
Of course if there were any chance that the buffoons in power in Westminster realised that we badly need a federal system of governance in the UK and offered the Scots real autonomy, that might just do the trick. But that would need world class diplomacy and all we’ve got is Boris so I think the dye is cast.