I wonder how Carl explained the death of Muntz to people if he did at all. It would seem pretty suspicious for him to come back flying C.M.'s famous blimp. Would people think Carl killed him? Would anyone ever believe his story of talking dogs and prehistoric birds?
I’d say most people would have forgotten about Muntz altogether. But, in the case you speak of, I guess people would think he died of old age(he was ancient :p)
Well, the talking dogs came back with him, so the evidence would have been right there. As for Kevin, I like to think that Carl and Russell kept her existence and whereabouts a secret, so that she and her babies could live a peaceful life without any other humans getting ideas about trying to seek out and capture them.
Since I’ve actually given this some thought, here’s my take on some aspects of this - and some more questions.
I think the generally accepted belief would be that Muntz died in South America years and years ago. I’m sure that back in the '40s, after several years with no word of him, eventually Muntz was legally declared missing and presumed dead, and his estate settled among whatever relatives there were. The state of the ship when Carl & Russell bring it back, though, along with the fact that the dogs are still trained and domesticated, might raise the question of just how recently Muntz was still alive. Carl wouldn’t lie if asked about it, but I don’t think he would volunteer the whole detailed truth, either. It would probably be sufficient to say that Muntz had gone mad after 70 years on the tepui, and died in an accident while still trying to hunt down his “monster.”
Obviously, bringing back the airship would get a lot of attention and publicity. Who, if anyone, would have a legal claim on it? Or have so many years passed that it’s just “finders keepers” and Carl and Russell retain some sort of ownership/control? My thought is that the airship ends up established as some sort of museum/tourist attraction in Carl’s town, and he is at least somewhat involved in this process. I think there is also some sort of home/sanctuary established for the dogs (some of them might also be adopted into individual homes).
I very strongly believe that Carl and Russell make a serious promise not to ever tell anyone about Kevin, because they don’t want anyone bothering her and her babies. The one person who gets to hear the entire story in complete detail is Russell’s Mom, who is also brought into the pact to keep Kevin a secret.
“Carl, you have some explaining to do!”
Yeah, I’ve never wondered that. But I have wondered what Carl and Russell would tell Russell’s mom and the police looking for Russell!
Agreed.
And, yeah, ellie-jessie-eve. Russel’s mom must’ve been freaking out the entire time.
Yeah, she got over it pretty soon though, I think she must of been happy that Russell gained a friend and mentor out of carl. You can tell at his Wilderness Explorer ceremony.
Yeah, she seems really happy for him at the ceremoney. It really is great that Russel got a mentor out of dissapearing!
By the way, my dad liked Up! Today we were talking about it, and he thought Russel’s mom was Phyllis… omg.
I’m glad to hear that he enjoyed it!
My theory on Russell’s Mom’s Reaction: In the “Up: the Insider’s Guide” book (the big DK picture book), there’s a “newspaper story” on the flying house that notes that “witnesses” to the lift-off reported seeing a “young Wilderness Explorer” onboard. And in the “George and AJ” short, we see that George and AJ see Russell hanging onto the underside of the house. So, Russell’s Mom may have found out that he was onboard Mr Fredericksen’s flying house - not that she wouldn’t still be justifiably worried and freaking out, but at least she has some idea of what’s happened to him. And when Carl & Russell bring back the airship, Air Traffic Control all over their flight path would have known where they were, and they were probably in radio contact, etc. I could see the police going to Russell’s Mom and telling her, good news, we found him, he and Mr F. are heading this way in an antique dirigible and should be home soon… 
I figure there has been major reunification, hugging and crying, Carl apologizing for accidentally taking Russell aloft, Russell trying to tell Mom all his cool adventures and looking for his Dad, etc etc before they even get to the badge ceremony.
But, in the movie, Russell states “Phyllis isn’t my mom!”
Good that your dad likes Up, though. It is fantasmic 
Here’s another Muntz-related question that occurred to me at some point:
When he’s giving Carl and Russell the tour of his trophy room, he says that most of his collection of discoveries is housed at various museums. What ever happened to those things? Do the museums still have them on display, or did they remove things or put them in storage when Muntz’s reputation was discredited?
Karly05: I’d say they were probably thrown in the storage room.
Yeah, I think so too.
That’s what I figured, too, but I’m glad to hear some other opinions. 
They might have been, but not necessarily. For those items that had been authenticated and served as a staple to some exhibit, what’s the point of storing them? Sure Muntz may have been the laughing stock of the scientific community, but why shove his good finds away because of one so called “blunder”?
Personall,y I think Carl and Russel showed them the dogs and perhaps all of his writings of Kevin and her labryinth to prove their adventure. All the artifacts, I assume,were sent to the local museum.
After just reading everyone’s comments (which were very noteworthy and admirable, by the way!), here is my own personal opinon:
I don’t think Carl killed Muntz. Carl did not plan for Muntz to jump out of the window of the house and fall to his death. Understanding and knowing Carl’s character, he would not actually plot and plan the death of Muntz, despite how bad the villian is. Carl simply wanted to save Kevin and return back with his floating house…but that also meant risking his own life to do so. It was Muntz’s rage, fury, and determination to catch Kevin, which was why he was so urged by his greed to jump out of that window after the bird. Carl, of course, didn’t know he would do this, nor did he ever think that Muntz’s leg would get caught in the balloon strings. In that scene, Carl just wanted to get Russell, Dug, and Kevin out of the house before he lost hold of it…and before Muntz would fire his gun at them.
Carl did not maliciously kill Muntz. The villian’s death was an accident, and I’m sure that if Carl was confronted once they reached the States again, he would explain just that.