Can rats make up after a bad fight?

Two of the rats I'm trying to introduce to each other had a very bad fight that got bloody. Now one seems to have a slight shift in his personality.

Quick introduction of the boys:
I never had any issues with M and L. M is more active and sociable and loves people, and L is a lot more low energy and prefers to sleep all the time, and isn't a fan of getting out of the cage, but will still come up and cuddle after a little bit of fussing. I got them 11 months ago, and they're both around a year old - not siblings, but they bonded pretty much immediately (like after the first 15 min together they were already happily cuddling). They were neutered together around 6 months ago. M always seemed to be more dominant. From what I've read about rat hierarchy, M seemed like the perfect alpha - just being a good, brave little leader, not dictator. Also, they've gotten a little big. Nothing too bad, but I'm more careful about their food portions now.
K hasn't been socialised with any rats that I know of (he was anonymously dropped off at the estimated age of 5 months). He's very sociable with people and first day I met him he was on my shoulders sniffing my hair and ear almost immediately.

Some background on how they were together so far:
They are of course in two separate cages, and I've been trying to introduce K to M and L through supervised meetings on neutral ground. The cages were next to each other, but separated by a piece of cardboard (secured in place with wires in a way that they wouldn't reach the sharp part). I figured that'd be a good way to have them learn each other's smells, without aggravating them through sight. Unfortunately, around three weeks ago they managed to partially pull the cardboard off when i wasn't looking. I don't know what prompted it, outside the cages there was slow progress (K clearly needed to be neutered, but I didn't think I'd have to hurry with it). The cardboard also wasn't a new solution, and it seemed to be working until then. But once they got rid of the cardboard in one spot, a pretty bad fight happened.

The incident:
I suspect M reached through the bars and scratched K (though the scratch was hidden well under the fur, and I only noticed it like 2 days later, despite looking very carefully) to which K retaliated, biting through the tip of a finger. Both injuries drew blood, and the second I heard anything I ran right to them. The finger wasn't fully severed, but enough that there was no saving the tip (there'd need to be stitches, and rat fingers are unfortunately too tiny for that). It happened at night, so I couldn't even take them to the vet (there's no emergency vet anywhere near), but I cleaned the finger with saline solution, and cuddled M until it stopped bleeding (which happened surprisingly quickly). The cages were of course immediately moved a lot further away. I took M to the vet first thing in the morning, and they confirmed that there'd have been no saving the tip. They just cut off the at that point necrosed tissue, gave him meds, and that was it. I set up an appointment to get K neutered asap, and for a week now he's been ballless.

The main issue:
I've gone back to trying to introduce them, and it's going noticeably better, but M seems to be acting different than usual. This goes both for when K is and isn't around. He's generally more mellow and seems a little submissive at times. The problem isn't just that he got hurt and could be traumatised (although that is terrible by itself), but I'm also very worried about the hierarchy. Like I said, M has been a very good leader, but now sometimes it almost looks like the other two are picking on him. Maybe I'm just reading into it cause I'm worried, but it feels like he was a lot more active before, and not as passive and basically letting most things just happen around and to him. Both K and L seem more easily aggressive, mean. Despite probably starting the incident, without the cage bars M was always very mild in his responses (he just got aggravated by the cage bars - from what I've read it's common). If K or L annoyed him he'd just pin them down for a bit, maybe forcefully groom them a little, and let them go - just enough to show who's in charge, and then move on unbothered. Meanwhile I've seen L pulling on K's skin unprompted (no squeaking), and K just keeps shoving his nose under both M and L to sniff their butts, or tries to mount them. Additionally K has noticeably more energy than the other two, and while I know that it takes time for the neutering to take effect, since the beginning he seemed a lot more needlessly confrontational than M and L have ever been. Yes, he's the new rat and he has to establish himself, but he's always trying something, even when the other two just lie down to chill. He keeps stepping on or under them, sniffing and nibbling at their butts, marking them with pee droplets, and just generally bothering them. Worst of all, M seems to just freeze up a lot in this position where he's on his hind legs with paws slightly above ground, and body in the shape of a ball, which isn't a sign of relaxation, and coupled with and very weak squeaks I'm worried he's tolerating more than what he's comfortable with, cause he's scared to properly stand up for himself. Also M has recently lost weight, and normally I'd be happy the "diet" is working, but L still seems pretty big. Their food bowl is at the bottom, and most of the time L just sleeps in the top part of the cage, so logically it should be the opposite, since M is near the bowl more. That could be just cause M does still move more than L, but alongside everything else it's just one more thing to overthink, cause stress could also cause weight loss.
I'm scared that if K does become the alpha of the mischief he'll mistreat M.
Should I intervene? Should I wait with re-introducing K and M until M seems mentally better (the finger is fully healed by now)? Should I spend some more one-on-one time with M to boost his morale? Will M ever go back to normal? Is there a risk he'll become an outcast and be bullied for the rest of his ratty days?