The bit I don't understand, is the companies merge to reduce overhead costs. Smaller companies struggle more, and have less financial stability. That model works just the same for countries, hence unions such as the EU. Telling people Scotland will be richer, well... have they considered the costs of funding all those extra managers, working parties, parliamentary committees, etc etc?
Scotland already has a government so it already has many of the structures in place
Scotland also pays lots of money to WM to manage these things UK wide. On independence we would have this money to spend.
To edit your analogy slightly. Big company has smaller office in different location. Smaller office is partly autonomous but things like payroll are done from head office. Smaller office brings in lots of revenue which all goes through head office which then gives a portion back.
Head office starts making really dodgy decisions which those in the wee office don't agree with but have to implement. Wee office decides to split off as a separate company.
Equally, long-term, it is not wise to rely upon one source of income. Oil is fantastic for now, but it is a finite resource. There is also tourism, which can be fickle as an industry, but will hopefully continue at least in its current form. Scotland needs a plan to develop other industries, and plans to develop trade agreements with other countries to export the products of those industries, be they physical or cyber, or...
"If you do not include oil and gas revenues then there is little difference in the figures - GDP per head in Scotland was £20,571 in 2011 and for the UK it was £20,873"
m.bbc.co.uk/news/uk-scotland-24866266
So without oil Scotland's GDP per head is broadly similar to UK. Oil is a bonus but not essential.
There are other small countries, with similar geography, who do well (e.g. Switzerland, Scandinavia). The cost of living there is very high however. Once the oil revenue stops, will it be similar in Scotland? And if so, would there be a 'brain drain' to other European countries, where intelligent, highly educated people would be able to have a better quality of life? You can't just look at the next ten years, but the next...
High cost of living compared to the UK perhaps. The people in those countries seem to be doing fine. There appears to be no particular drain drain from Switzerland/Scandinavia to the UK where cost if living is lower?