Thank you all.
So the 100,000-year-long war ought to be much shorter, or is more allegoric. Maybe both sides concentrated only on each other and ignored every other race. Otherwise the war would intersect with several events, some canon and some mentioned in other books.
This means the Grigari are still around. A race that can kick the Borg around?
Now that I am thinking about it the original story of STO was supposed to have a enemy from the Beta Quadrant - a connection?
Is it possible that they will be an enemy of the 25th-26th century UFP?