I think he could do it, but I think it might have unforseen knock on effects. I used to work for Disney, and even as an adult if you're not actively preparing for it, it can be a bit jarring the first time you run into Goofy headless at the smokers table. And I was one of those kids that, even on my first trip to Disney I knew it was someone in a costume, so I couldn't tell you if anything would be lost for some kids, maybe it's like Santa? And Disney pretty actively discourages cast members from talking about this stuff - "what if a five year old is in earshot" and "don't ruin the magic", they taught euphemisms like "close personal friends with [character]" if you, say, wanted to talk about your friend who is close personal friends with Tinkerbell. And for as much of a soulless company as they are, Disney (at least 15 years ago) actively cared about crafting an experience in their parks, there is so much detail that people don't realize is going on. Not acknowledging headless Goofy is part of that.

Being honest to kids is still probably more important than whatever bit of magic we all lose by doing so.