Not gunna lie, the thought almost makes me want to cry. I'm a born and raised WDW-er, half the reason my family moved from Illinois to Florida when I was like... 3 months old is because of Disney. My mother believed in the Disney magic and I was lucky enough to have visited the parks with her while she was alive, our last family vacation before she passed when I was still a kid was to Disney, her most favorite place in the world. And I thank that trip all the time for cementing a childhood dream of wanting to work for the Mouse. So yeah, a world without Disney, would be absolutely depressing.
I mean, even if we take out the themepark part of the equation and are left with our loveable characters, and all the merchandise that follows them, it would still be sad. There would be no magic, no wishes come true, none of those lovely catchy songs that you sometimes curse when they get in your head (I have never watched Phineas and Ferb a day in my life and one of the songs from that show is currently looping in my head.) Yes yes, it can be argued that Disney only gave us Broadway-style retellings of fairytales that already existed, but they also told the stories in ways they've never been told.
So if we take out the theme parks, princesses, winnie the pooh (A.A. Milnes, not Disney), anything that was not an original Disney story, yes we are still left with a decent chunk of stuff that has defined generations.
Are things perfect? Nah, there is no such thing as a perfect company yet. But Disney has definately made things a lot easier. Mickey came around at a time when people just generally weren't happy, right? (I have no clue if I just made that up or not, I can't remember, but wasn't he depression/ww2 era?)
Either way, a world where saying "Have a magical day!" would get you the weirdest look ever, would be the most depressing thing ever.