Arguably, Kosovo should be an independent state (or leave Serbia and link up with Albania) because the vast majority of its population are Albanian.
The Basque issue is clouded byt the fact that there are many non-Basques living in Basque lands.
Northern Ireland is another issue again. The majority of inhabitants of the Province wish to remain British, a minority wish to join the Republic. Demographic changes over time may eventually favour the republican side. For the moment democracy should prevail and NI should remain British. Note - as far as I'm aware there is little / no suggestion of NI going it alone as an independent state.
Each of the examples you give is different, unfortunately you just can't generalise.

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