Draekai
Wait!! I got it!!!! The Earthen plane doesnt exist.... Lin lost his connection to the Earthen plane.... We learned this story is based on a multiverse.... The portal wasn't to the next plane. It goes to the spiritual plane in a completely different universe. One in which the Earthen realm doesnt exist.
I wonder if the old lady is Origin? Lin's sacrifice could be him as a supreme god trying to save Origin or minimize the damage from whatever caused it to start leaking. Could also have something to do with Lilith's mother killing gods. Apparently, Supreme gods are spokespersons/hands and feet of origin. After eons of Supreme gods working for her, I wouldn't be surprised if she viewed them like her children. In that case, for this theory, Lin would basically be her golden child which could be why she was so lenient on Lin getting back to his duties(she did say he needed to get back to his duties, but Lin declined and pretty much said he'd rather relax with his disciples)
Let me guess, Earthen plane is supposed to be a battlefield of Gods which was seemingly destroyed in the fight of gods but Lin kinda protected aka sacrificed himself for it and kept it secret from other planes The Old lady is probably Origin and Lin is her favorite god or something She said that Lin sacrificed something.. So maybe he did something for the earthen plane