I've enabled for guards to be recruitable with swords and I've had one following me for a while, while i was still building my house one day he just vanished! Now idk if he got killed or despawned or he might went to a nearby village, but if he did despawn this is very frustrating, would you be able to know? Are they supposed to disappear if they follow for too long? Or is it a bug?

This seems to be a bug. Try to recreate it and post the steps here.

Ok it'll probably take me a while

Ok so I've tried to recreate the bug, I've had several gaurds recruited, i gave them each different positions, and some let them wander around, I've waited several ingame days (probably not long enough tho) I've also traveled away for a bit, and logged out and back into my world, as far as i can tell they don't seem to despawn, however i did notice that without a village nearby those that i let them wonder around tend to wander TOO far away and randomly go places where i wouldn't be able to easily find them in survival, so that might be the issue. (But I'm not 100% betting on it)
also unrelated i noticed that if i arm them with a musket they seem to get really confused if it's a melee or a ranged weapon... Sometimes they fail to reload, And they also friendly fire TOO often, that's really annoying :(

also unrelated i noticed that if i arm them with a musket they seem to get really confused if it's a melee or a ranged weapon... Sometimes they fail to reload, And they also friendly fire TOO often, that's really annoying :(

Make a separate issue and this can be investigated
Keep in mind that the musket compatibility only works if you're using the latest 1.20.1 or 1.21.1 forge or neoforge version