It doesn’t really matter if a theory sounds too unlikely or outlandish. That IS the fun of it, after all! Plus, those make for really good discussion starters.
I’m guessing Yeti was just so pleased to have his own kind around that he didn’t bother really getting into many details–apparently, he was just interested in being a good host!
Also, your theory about the Himalayas door being used repeatedly for banishments definitely sounds likely! I’m thinking this is how Yeti came to meet Bigfoot before he travelled off to the wamps or woody areas, where most of his sightings have been reported, to escape the blistering cold and fashion himself poison ivy diapers to wear on his head. But that leaves me wondering about Nessie and how he might have traveled from the snowy mountains of the Himalayas to end up in the Lock Ness lake in Scotland. =p
Maybe the door to the Himalayas is not the only one used for banishments. There may be a few other doors leading to separate places, such as an impenetrable swamp or any other location in our world that provides the roughest environment possible so as to minimize the chances of survival by a monster.
Maybe Mike went after Sulley just moments after and Yeti didn’t catch him by the time he came back from making snow cones. OR Yeti probably had his reasons not to go back with Mike. There are a bunch of theories going around in my mind as to why he wouldn’t want to go back! Unlike Sulley, Yeti might not have had a strong enough reason to try to get back to his world or might have been too afraid to do so. Maybe the situation he had gotten himself into in his world was enough for him to realize that he had gotten off easy with banishment. Maybe his misfortune was a result of a sheer accident and now he “knows too much” for comfort and someone decided it was too risky to keep him around the Monster world. Now I feel like this is going to turn into a mob thing–Yeti was afraid of getting whacked or something if he went back. =P
Yeti strikes me of being more of a maintenance guy or something minimal rather than a Scarer if he did work at MI. He’s got the right build to make a good Scarer; however, that may not necessarily apply to his abilities and he might have actually ended up being worse than Phlegm!
Ever since I saw that scene, I will always keep believing that he fooled himself into thinking that the place he was banished to truly really was wonderful in order to keep himself from breaking down like his buddy bigfoot!