[Larry-AV]

Here are three of the major issues.

If Scotland splits it will, if it chooses, have to apply to join the UN, the EU and NATO.

No problems with the United Nations, Scotland would become another ordinary member. The UK will retain its permanent seat on the UN Security Council and if the UK was to totally dissolve, then England will inherit the role the UK used to have.

With the EU Scotland would have to accept the terms of membership for any new applicant state, which include :
1} Using the Euro, with no opt-out to use sterling or its own currency.
2} Joining the Schengen treaty on open borders between Schengen members ... and border controls with non-Schengen member States, specifically, the UK and ROI.
3} Scotland will not inherit the rebate the UK gets and as with the UN, if the UK dissolves, England will inherit everything the UK currently has.

With NATO Scotland sans nukes would be yet another small country happily sheltering under the ultimate deterrent provided by the USA/UK/French nuclear umbellas, whilst hypocritically denouncing nukes !