Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
- This is why he wants to be Mukohda's familiar. The Online Supermarket is the only thing that can eventually restore him to the God's Realm.
- Fel didn't track down Mukohda for his online supermarket skill originally. He only wanted the delicious food Mukohda was cooking, and followed Mukohda for his being able to sate him with a comparatively tiny amount of meat. However, he just seems to be an ardent follower of the pantheon's religion. The God of Creation would not have been all that happy if Fel was trying to work his ways back into the pantheon by consorting with the other gods, and if Fel was a fallen God, then he would likely be trying to claim Mukohda's abilities as his own to gainf avour.
So who is running the store? I can only speculate, thus the WMG, but I think it's a higher being that's in charge of all worlds, and figure Mukoda needed a leg up. We'll see.
- Maybe the store isn't actually a store. It's something like the appraisal screen, instead, and something created wholly from magic. If there was a deity or other measurable power operating it, Mukohda would not be able to just add stores by levelling up. In terms of function, it might be something like a replicator from Star Trek, with the "store" being a simple interface, and the objects being materialised with magic, allowing them to have effects that don't exist in our world.
- The kids had escaped long before the kingdom fell. It's not as though their escape, and revelation that the kingdom was using slaves as troops is anything particularly new. They could have just been killed by a monster, and the effects would be much the same.
By giving him the "Perfect defence" skill, the deities showed that they would not be willing to let Mukohda die, taking their supply of otherworldly goods with him. That may also hold true when he starts getting old.
From "Old Stories from an Older Dragon", we also know that Mukohda has been more or less travelling around, unchanged for at least 400 years, by Gon's last recollection.
Mukohda's own familiars would be unlikely to want to see him succumb to the downsides that come with age, and would likely petition the gods on their own, if they had to.
Granted, while most of that is due to him cheating with his skill, even then it says something about Mukohda that Agni, Rusalka and Demiurge enjoys the dishes he occasionally sends them as per their requests or by his wishes.
1500 years is also quite a long time for anything to happen to him, during which he could, at any point, enter a state of apotheosis, most likely due to the Gods and Goddesses (and/or his familiars) not wanting to lose their access to other world stuff and his cooking respectively - or alternatively, he could start turning into a God (by sheer accident, lol) through accumulating enough experience over the years, or from having his many achievements later getting warped into the stuff of legends to the extent that countless people are now worshipping him for whatever reason that might seem plausible.
It would end with Mukohda realising that he actually doesn't mind it, since he now can happily spend his time incognito in the fantasy world like he originally planned to, in between hanging out with his familiars and continuing his offerings to the other divine beings out of habit.