If I were to make an overall suggestion about Bijuu and RP relations,
1. Remove challenges - This is something many a people have said, and it makes sense. If the bijuu are there to stimulate RP, then challenges which are outside of RP don't help at all. The only point I could see to them in the first place is that it gives someone without sealing techniques the ability to obtain a bijuu. To solve this particular point people could get over it. If more seal-type characters need to get involved, then that's good, it's just more stimulation for RP. Whether or not people just randomly add sealing to their characters... well, that's not something we can deal with with any more than a slap on the wrist.
2. Responsibility- I believe if you take on a bijuu, you are assuming the responsibility to the site and others to roleplay. In that sense, any large leave of absence for any reason should result in a bijuu being removed, as otherwise it isn't fair or fun for the other players. I would say that 2 week inactivity would be the limit here, without really good reason. Real life was busy is not a good reason, as I guarantee you that anyone could find at least a minute or two to log on within 2 weeks.
So what do you do if you got your bijuu taken away and you want it back? RP it back, go take it from the person who got it. Shouldn't be too hard, right?
3. Ownership in case of absence -
If the participant was in a battle when he went absent, the challenger receives the bijuu.
If the owner was not in a battle, then the leader in his CLAN, which may or may not be the village, receives the bijuu. A clan will be the assumed as the clan they are listed as in game, which will usually be the village -- this is to keep any retroactive decisions from arising if they were part of a separate "internal clan" or something. If that were the case, then they should have just made their own clan and gave it affiliation with the village.
If the absentee was not part of any clan, then the beast is in a free for all position, the specifications of which (tournament, mission, war, etc.) is to be decided on by majority rules within a one week time period after confirmed removal of the bijuu, and to be acted out within a week after the decision.
Do these make sense?