If you’ve got 40 people depending on a single piece of relatively inexpensive hardware, a spare for the future would be highly recommended.
If you can function without zerotier, I would wait. If I were in your shoes, I’d be building from source all the time (control of what I build and faster security by a couple days) and testing on a second router. That’s what I do at home, even more important in a business environment.
Downgrading would not be my choice as it increases the possibility of a config issue.