So, could the project get along without *new* editors? Probably for a while. But editors move on and stop editing -- there's a pretty high churn on Wikipedia. It would be harder and harder for the editors to keep up.
It's also a loose-knit group with a lot of conflict that is resolved on-wiki. As people leave, it's harder to do that resolution.
Gradually, the content would suffer -- which would mean even fewer new editors.