If the reduction in maximum HP does not recover naturally, you could just bite the person once per day and wait for the regular damage to heal overnight.
Unless it's a matter of a PC being turned into a vampire, I'd just be inclined to handwave it.
In this homebrew, will it be possible for a PC to become a vampire, and if so, will it be possible for that PC's player to continue playing the character? If yes, I can see the need for rules that work. If not, then I don't see any hard and fast rules being necessary. People become vampires as the story dictates.Its a matter of me being busy writing up a homebrew that is about vampires. I'd like to change as little as possible from the vampire entries in the monster manual, but I am really struggling to not change the requirements to create a vampire.
In this homebrew, will it be possible for a PC to become a vampire, and if so, will it be possible for that PC's player to continue playing the character? If yes, I can see the need for rules that work. If not, then I don't see any hard and fast rules being necessary. People become vampires as the story dictates.
You could always rule that a vampire doesn't have to keep biting an incapacitated target (it can stay latched on, as it were) and thus just deal the blood-sucking necrotic dmg without also having to deal the piercing dmg.
A humanoid slain in this way and then buried in the ground rises the following night as a vampire spawn under the vampire's control.
How is it still an issue? If the victim is at 0 hp, that piercing dmg will just result in two failed death saves. But if the vampire then stabilizes the victim, those death saves will go away and it can just suck the blood without worrying about accidentally killing the victim through automatic failed death saves.That is really good! I was just planning on having anyone killed by the bite come back as a vampire, but your way sounds much better. The only issue would be the initial piercing damage.