Regular Guardians (not Elder Guardians) that have been named by a player with a name tag will still despawn if you get too far away from them, like any unnamed hostile mob.

I expected the Guardians to not despawn, as all other mobs that have been named with name tags do not despawn.

Steps to reproduce:

1. Name a Guardian with a name tag
2. Move far enough away from the Guardian so that the chunk that it is in unloads
3. Return to the chunk the Guardian was in
4. The Guardian will have despawned