In addition to a United Ireland, I expect that Scotland will eventually secure the Independence which every other civilised country has as an unquestioned right.

With regard to what flag will replace the current "Union Jack" ("jack" is really only appropriate for a flag at sea, by the way), well, it's long been a slogan that "There ain't no Black in the Union Jack", so perhaps another appropriate national flag for the Red Cross of St George to be superimposed upon and visually cut to ribbons would be that of Jamaica; similar in pattern and proportion to the Saltire of St Andrew, and certainly more colourful. All the benefits of being both familiar in its components and new, not to mention inclusive and pluralistic and multi-cultural.
Run it up the hypothetical flagpole and let's see who salutes.