That estimation is not a very good one, really. Most of VMX is the same inspired silliness that made the Muppets famous. Even in the "alternate universe" there's still some very funny moments--such as Gonzo's dancing brick, Animal river-dancing, and Johnny Fiama bartending. You really should see this movie before assuming anything. You know what they say when you assume things...
And there has been sadness in most of the Muppet movies! TMM had someone trying to kill Kermit, GMC had Miss Piggy in jail, MTM had the Muppets going their seperate ways ("Saying Goodbye" is the saddest Muppet song ever! ! !), MFC had Kermit worrying about Miss Piggy's safety, MCC killed Tiny Tim (albeit only in the preventable future), MTI Jim's life is pretty pathetic, MFS Gonzo hugging Kermit and saying, "You're the best friend any alien could have" and Kermit responding, "We... We love you Gonzo" is some of the most heart-wrenching stuff out there!
So don't tell me that Muppets and sadness don't mix well, because it's an old plot idea that works very well.