Here's the thing. If they did give Maria a send off, Luis is still on the show and got a new lease as a character via the bike repair shop. Think of that message, even if unintentional. He's wearing a fedora now. Try and tell me it wouldn't imply he'd be the depressing yet sleazy guy trying to get younger woman to replace his wife. I'd tend to think that Maria would be given the illusion of being "still there" but not actually appearing. If both characters were said to move away I'd agree. There's just an unfortunateness to the wife leaving and the husband staying that even the smaller ones would pick up on.
The only characters I can think of that actually got the send off were Hooper and David, both for reasons we already knew. Everyone else that left just...
left. And while you can hand wave some of the short lived vast as coming and going, you have to admit the disappearance and complete "sucked into the void and forgotten about" of some of the longer time members is jarring. Linda especially. She was a staple character for quite some time and then she just ...stopped. And not even a nod or reference to her existing. Heck, the entire Around the Corner disappeared and it was less awkward. (Is Sesame Street located that close to Elmore?) Even if there were a logical way to send Maria off on the series without making it depressing about Luis, it's not like they've had many for any other of the characters. A shame they don't, but that's how it is.
I'm sure that's true to a point, but Bob has gone on record in both newspaper interviews and in I Am Big Bird to state that he now views Sesame Street more like a hobby than he does a job because he is not called in for more than an episode or two per season. So, it seems at least he is available to work more than they are calling him in for. Plus, the likes of Gina and Gordon are obviously available to work because they are there on the set, except they are extras in the background.
I'm not going to completely doubt that it has something to do with kids relating to younger adults. I mean, when the show first popped up Bob and Gordon and Linda were the young adults (20's and 30's young) that were the not quite parental figures (friends of parents) that acted like friendly teacher types/young adult relatives to the Muppet characters, and even the audience. Maria pretty much was the cute college age girl that little kids develop their first sort of weird "I don't understand the age barrier" crush on (which I'd say Gina, then Gabby, and now Leela filled as the show progressed). David and Luis at the time were the not quite college going teenagers, not quite Bob and Gordon age funsters (Chris and Mando today). Hooper was the not quite grandfather figure... maybe older uncle. That's a role I'd see Bob and or Gordon in today. I think there is lost opportunity for Gordon to mentor Chris, and that's sort of the role Alan plays. I agree. It's strange, though, that Gordon was the go to adult for the several seasons up until just recently.
It's a shame and unfortunate, but again who thought this was going to last 10 years, let alone 46? There was a huge learning curve and still is. I'm glad that they didn't replace characters willy nilly giving us a sort of Maria and a maybe Bob. Gordon's change was for the better, I think and they got
very lucky with that one averting the "you don't look like you" he could have.