Well... since we've seen tanks and such as well as Landing Craft, that does suggest that Abyssals have their own equivalent and sometimes land forces. So you could have Miho fighting Abyssal Tanks and landing forces...
One possibility is that the lines between something the Neuroi and Abyssals are doing get crossed and cause the whole incident, with the GuP world being whacked as well.
Heck, maybe the whole incident causes a section of the three worlds to intersect somewhere and you can get people crossing from one world to another. Which, of course, would be highly interesting for both the Abyssals and Neuroi. You got the GuP world untouched by war and full of resources which both the KanColle Earth and SW Earth need. Both the GuP and KanColle Earth has technology that SW Earth could use against the Neuroi, and the SW and KanColle Earth would likely have knowledge of magic that the GuP Earth does not, especially with the threat of both the Abyssals and Neuroi out there, when h even the closing of the portal would not solve.
Of course, until everything gets sorted out, you got our three protagonists trapped in the middle...
