Maybe instead of dying at the end of last year he somehow ending up in the network as a higher form. The whole thing could be about getting revenge, we know how much Trek villains love revenge! It's a hell of a coincidence to lose a character called Gabriel then have an Angel appear the following year.
I don't think so, because I think the Red Angels are going to involve the return of an established Trek species like the Iconians or more likely the Preservers. One of the showrunners did mention an old Trek species making a return on the show. As far as Lorca goes, I did think they left his "death" ambiguous by having him fall into the giant sporeball of doom, just in case Jason Isaacs decided to come back, so I wouldn't rule out his eventual return or anything.
It would be hilarious if real Lorca actually thrived in the Mirror Universe, taking on the identity and reputation of his Mirror self, and by the time they find him again he's already Terran Emperor.
Lorca didn't even technically fall into the mycelial orb of doom, though. He got 'bug hits windshield' vaporized on the containment field surrounding said orb. This is before the field gets dropped by Burnham.
The Red Angels are Connolly. He was scattered through all eternity when he hit that asteroid and exists everywhere at once.
I hope not. It's something which, while possible and arguably in line with creative decisions made by the show so far, would be very poor writing, so I hope it's not the case. But I think at some point we will see Prime Lorca.
An imprint of him could be in the Mycellial Network. I'm not quite sure how you from that to Red Angel... but why not? "Saints of Imperfection" was pretty nutty but somehow it still works. Soooo... why not stay in this zone? "Lorca's no angel!" He is now.