We lost our key from Deckert's a couple years back, so this was a problem that was through no fault of the company. When Mom phoned them (during business hours granted), they gave a quick solution to get another key, at no cost to us as far as I know. This solution involved me walking to an on-site location, which would have been very difficult for my mom to do herself. I am not sure how they would have handled it if everyone in the party had been disabled, or how quick it would have been, but it doesn't sound like that will be a problem for you.
The scooters seemed to be new and I don't recall ever reading about any off-site company's scooters actually malfunctioning (I have heard of Disney's ones breaking down). But I guess technically any piece of machinery can malfunction, so that's a fair question. That said, I'd be rather surprised if a scooter from Deckert's needed a replacement battery. I believe you are supposed to charge the battery nightly (and maybe take the cord along with you just in case). But it was only after going for 2 full days without charging, that the battery gauge on my mom's scooter went down one tick (out of probably 8-10 ticks; I didn't count them). It was still completely in the green zone. So I think the batteries are new enough that IF somehow they stopped working, the problem might be mechanical, not the battery itself.
But again, I don't recall hearing of ANY off-site company having such problems.