It's fairly simple for me. The Borg assimilated Earth, so no Columbia visit to Erigol. But by the time the Borg assimilated Earth back in 2063, Mantillis was already back in time and had become the origin for the Borg. And according to the Caeliar, this was a normal part of history and always happened. Why should the Borg then cease to exist because of a change that happened after it came to be?
Basically, ignore that the Mantilis in the past no longer has an origin and just accept that it is.