Scotland to become independent 'within 20 years', says defeated nationalist

Scotland will break away from the United Kingdom within 20 years, the defeated leader of the Scots nationalists predicted on Sunday, after a poll showed a majority of voters would back independence if another referendum were held today.

In September, 55 % of Scots voted to reject independence in a historic referendum after Britain's three main UK-wide parties promised to grant greater devolution to Scotland in the event of a "No" vote. But in a surprise poll on Saturday, 52% of those asked said they would now vote for a breakaway.

I believe that will become true. As their population ages more and more of the youth vote will matter. Younger people were those who supported that Scottish referendum.
What would the Scots gain by separating? Wouldn't they have more of an economic burden separating from England? There has been a high unemployment rate in Scotland. What happens if they run out of oil? What other ways do they have to make money?