"Many have neighbours that would be unwilling to assist the UK."
Which?
Don't give us Nation X, Y and Z. (And OK, you've distracted me. Why wouldn't the US, Spain, Italy or France help with nation X in your scenario? What nation X doesn't have a neighbour or near neighbour that we couldn't use? What nation X without neighbours who would support UK AD aircraft could we operate against without needing land based AAR, ISTAR, etc.) No more what ifs, - real world examples only.
Your first real world example was Sierra Leone. Jags were already on Ascension, ready to deploy forward to Senegal. Ghana and Cote d'Ivoire were also available.
Your second real world example was the Falklands. There's an airfield there now, y'know, with AD aircraft based. No need for a carrier to defend the islands now!
Your scenarios 4) and 5). The US contribution (or the French, or the Spanish, or the Italian) would be to provide the required AD, if we couldn't provide it using land based assets operating from adjacent nations.