A roadside replacement is genuinely a cinch - you only need two small tools or something, and you can loop the new belt on, admittedly a bit of an arse if you don't have someone to push the bike for you as you probably don't have a centrestand.
Don't all Zeroes require disconnecting the swingarm to replace the belt? And compressing the suspension using a ratchet strap?
Some people had pre-threaded and tucked away a small limping belt they can unfurl onto the sprockets should the belt snap (threads somewhere on this forum).
My '16 FX has only 12,500 miles on it and the belt still looks good. I like to hop speed bumps, so years ago I bought a spare belt just in case, but don't carry it with me. After all, the bike is rarely more than 25 miles from home.