I was thinking about this recently and can't think of many downsides for the Tories if this was to happen. By almost all accounts Scotland and Northern Ireland cost money, they're also areas that send no/very few Tory MPs to Westminster. Without Scotland and NI the Tories would have an almost unassailable grip on power. Also there actions show very little regard for these two countries, they don't seem to care what they think or how actions in Westminster will affect them.