K9's (And Romana's) return from the CVE?

I just watched Warriors Gate a week back, and I was reminded that once K9 went through the mirror, he couldn't come out again (Was that just an indication he couldn't return to ESpace, or was he also unable to return to Normal Space?

I'm listening to Galifrey Adventures Audioplays S5 now, and K9's appearance reminded me about that statement in Warriors Gate. Is there any Extended Universe story that tells the story of Romana and K9's return from the CVE to Normal Space?

 

Their ability to travel through the CV was covered in Terraqnce Dicks' 7th Doctor novel Blood Harvest (which relies on there being a conversation between the Doctor and Romana before he departs that can't happen in the screen version of Warriors Gate, but is there in Steve Gallagher's novelisation). I don't think ther's ever been any explanation of how K-9 can work back in N-space though.

 

E space reminded me of The Great White Space of the Cthulhu mythos

 

There's also an offhand comment in Zagreus: when Romana sees the mirror in Rassilon's Tomb, she comments it's like the one she and K-9 took out of E-Space.

 

I wonder if Rassilon was the inspiration of F. Paul Wilson's Rasalom (Molasar) from THE KEEP and NIGHTWORLD.