In regard to any effects on Oscar from him having been in the void for a month, you would be best off asking Add's player Lavvy.

As for what would happen to Oscar after returning from the void, he would be swept up by Heaven's representatives that are still investigating the temple and area. He would be checked for general health and corruption, offered a bath, meal and change of clothes, then carefully questioned for any information that might further the investigation into the incident.
Once all of that was finished, he would be released back to the care of his Goddess.

If you require more details, feel free to message us again!