It is possible that a gandhabba may stay in the para loka as long as it feels it suitable, eg. The reason why a gandhabba descends into the womb is because it wants to re experience all those pleasant memories of being a child, being loved by their parents, growing up, going to university, going hiking, smoke, eat pizza, fall in love, have sex, getting married, having children, having grandchildren etc.
However if due to karmic conditions, their stay i para loka is more pleasant than that. They may just stay there until that pleasantness runs out, at which point they would long for going though the whole of human life again, but with a slight twist. Just like if you liked the last Marvel movie, most of the time you wouldn’t watch it again, but instead watch the next Marvel movie. it’s the same kind of movie, but with a different story.
If however, you where watching a movie and suddenly the power went out, you would want to return to it as soon as possible. This is the case for those rebirth accounts that had a sudden death. The gandhabba feels as though it didn’t get to experience what it wanted, so it want’s to get back to where it left off as soon as possible.
When it comes to people seeing Jesus or whatever kind of deity of their faith. The way it interpret that experience, is if someone had genuine faith, in let’s say Jesus and lived their life as if that was a reality. Then they would establish an energetic connection with Jesus in the Brahma realm. And if they lived a meritorious life with faith in Christianity, at the point of death the vipaka of that merit will come back connected to ones faith. Meaning that the Brahma Jesus or some Angel, or another Brahma would send them energy, and the gandhabba would dream up a form to interpret the experience of receiving that energy, and hence see a sphere being of light, Jesus or an Angel.
If it was the case with a Hindu Brahmin who worshiped Brahma, they would see their depiction of what they thought Brahma looked like.
If someone worshiped Zeus, and lived a meritorious life according to that faith. I would speculate that they would actually generate a connection with Sakka. And if Sakka helps them out energetically at death, they would see that as Zeus.
If someone worshiped a deity that didn’t actually exist, but lived a meritorious life with the belief that it is real. I would suspect that you may be connected to a deity that represents those same qualities.
If they had believed in an immoral deity like Moloch, and committed child sacrifices to him. Then when they die and they get that vipaka associated with the sacrifices, they may see that as the form of Moloch coming to help them, and they will grasp that, and in so doing they will end up in lower realms.
The reason i see it this way, is because the mindset and belief you do kamma with, is in accordance with the vipaka you receive back. So if i believe in Jesus and do good things in his name, then that vipaka would be connected to Jesus in some way, either by representing similar qualities, a connection to the Brahma Jesus, or connected to other beings with faith in Jesus, or leading one to the path of Jesus, or reminding one of Jesus and what he represents for that person.
When it comes to the argument that, since so many people die all the time, such a deity would not have enough time. I don’t think that applies, since a deva only needs to send that gandhabba some energy.