In my experience this turns out either one of two ways. They will either continue to scuffle until Magneto finally gives up, which may be after Xavier exits puberty, as he is still growing he is certainly still in puberty, or it could end in a horrible fight that warrants them being permanently separated.
From my experience with boar pairs it often becomes quite apparent who can and can't get along quite early, if it is going to escalate into a horrible fight that *typically* happens either when they are first introduced or within the first 2-3 days following introductions. I have had one instance in which that wasn't the case, but that involved a boar who was roughly three weeks old when introduced who caused big issues with his cagemate once he hit 6 months, in that particular case I did have to separate (it was the older boar who was worse injured, along with my hand, but all three of us healed well) and both boars were successfully re-paired with their now permanent boar cagemates.
I would give them more time before deciding what to do, in the video it is at least a promising sign that Magneto does not try for another nose-off or approach Xavier after the chase. Some of my now successful boar pairs had quite a rocky period for the first three weeks before things mostly settled down, aside from the occasional minor scuffle.
If both are determined to be top pig more space might not help, but it does give Magneto more space to maneuver away if they end up in a chase again, I'm sure you have noticed it gets worse once Magneto is cornered during a chase (this is where the wider cages sometimes helping comes into play).
I wish I saw this a bit earlier. I went to bed (it's 2am here) and it's almost like as soon as I turned off the lights, they started fighting started again. I did what I did the other nights; just ignore them and tell myself that they'd sort it out and I should leave them be unless I heard one obviously in pain. But for over half an hour I heard nothing but ruffling hay, bodies slamming into coroplast walls, chattering, snorting, and the occasional whimpering. There was an occasional pause here and there but after a minute or two it'd start up again. I spent the evening convincing myself they were making progress because there was only one instance where Magneto get scratched on the mouth that was bad (he didn't even whimper). Otherwise they only squared off every twenty minutes or so, and it was only very briefly. It may have been because every time they looked to start something, I'd gaze over them with a T-shirt ready, who knows. If they didn't spill each other's blood or otherwise injure each other on 3-4 separate occasions the story might be ending differently.
Maybe it was the fact that I haven't gotten any sleep since Saturday because their fighting would keep me awake at night and wake me up in the morning and now I'm just cranky. But I grabbed Xavier and put him in the KayTee cage (along with bedding, hay, bowl, water, etc.). Tomorrow I'll call up Boston ARL and assuming no epiphanies happen, I'll be giving up Xavier the same day or on Friday. I'll clear my head a bit, let Magneto de-stress for a little while, then figure out where to go from there. Again, I still want a friend to him but maybe this was just a bad personality fit. Things I learned:
1. Bigger cage seems to be a good way to resolve issues. I'll have a few extra grids and coroplast on hand just in case, though again, expanding the cage is going to be difficult. My roommate joked that I should just take one of the living rooms (we don't really use them at all) and let them loose.
2. I failed when adopting both in asking the owner about their temperaments. Magneto's owner might've provided insight into how he behaved around his old buddy. Even if the shelter couldn't tell me anything, I think I should've watched Xavier a bit more to see how he was. He was the "cutest" one there and that was my main criteria. Though I don't know if I could've foreseen Magneto's stubbornness (I guess if both are dominant, it'd be a bad idea to put them together).
3. I should've came to these forums to get some advice first.
I placed the two cages next to each other so they could see each other a bit more. They were squeaking at each other; there was some rumblestrutting but no chattering. They climbed up on the bars and sniffed each other a bit. Then Magneto walked away into the pigloo that I put back for him and Xavier started chowing down on his hay. Then he curled up in a ball (which I've never seen him do as he usually plops straight down). Does he know the jig is up?
Either way, thanks for all of your help on this. I know I made some boneheaded mistakes but I learned a lot about guinea pig behavior through this experience. Once I clear my head and am ready for another companion search, I'll start a new thread.
Hopefully I'm doing the right thing here. I guess one last question is: am I being too hasty in giving up? I suppose if I use the living room I can keep these two separated (Xavier would move into the Midwest habitat, of course) and next to each other for a few months until Xavier passes puberty; this will give me enough time to regroup and get some supplies to expand the cage. but I don't know if that's just the sentimentality in me speaking now.