I suppose in a case like that, you could have excess cars from outside of the area drive into the evacuation zone to alleviate the shortage. Imagine a swarm of a million robotaxies driving in.
That would be a bad idea. In evacuation situations, they normally make the roads be one-way out of the problem zone. You can't do that if you have cars coming in, which means you have now halved the rate of the evacuation to accommodate the swarm of robotaxis.
That said, what will it be like if you want to go camping and don't want to unload the car completely, because say you're doing several camp sites.
Long-term (multi-day) rental or owning is often the only practical choice.
People think they are special and they have legitimate needs that can't be met with robotaxis etc. I'd be willing to bet there are a million carless people in NYC who moved there thinking they would always own a car but figured out otherwise when they factored all the costs in.
Only about 81% of the U.S. population are in urban areas. Only 71% are in urban areas with a population over 50,000 people.
So somewhere between 19% and 29% of the U.S. population are special, and have legitimate needs that can't plausibly be met with robotaxis, because they live in areas that aren't dense enough or populous enough to have taxi or ride share services, much less robotaxi services.
Remember that for every New York City, there are a hundred Bucksnort, TNs.
Also, you're ignoring commuters entirely. The longer the commute, the less likely it is that a robotaxi will be able to do something useful while waiting for you to return, and the more your trip will cost. In dense urban areas with people commuting single-digit miles, that probably isn't an issue, but even in semi-suburban areas like most of the Bay Area, it can be a problem.
Uber/Lift is great for certain situations, but bad for others. You don't have privacy like you would in a robotaxi, you're limited by who is willing to pick you up, etc. The cost of robotaxis will be much less than uber/Lift, and that will be a very compelling argument for most people.
Why? The vehicles will cost a lot more, and most of the cost of service is depreciation on the vehicle and maintenance thereof. Yes, the maintenance will be cheaper, but that doesn't help if the car costs twice as much. The driver is only a small part of the cost. Fuel/electricity, insurance, depreciation, maintenance, and profit for the ride sharing network can easily add up to 75% of what you're paying for Uber or Lyft, and that's before you factor in the car costing twice as much.
I doubt you'll shave off more than about 5% when all is said and done.
Nobody is going to sell their car to switch over to using solely robotaxis, but they will not buy a new car and instead use the service.
If they have a car, why will they bother paying more money for the service that's less convenient than having their own car there? Just to not have to drive? I mean for some people, maybe, but I think a lot of people will say, "Yeah, or I could spend $45k on a Model 3 and have the best of both worlds."
I don't think robotaxis will be like current ride hailing. I think it will be a subscription. I believe you will pay something like 200-300 a month for access to the cars whenever you need them. Will it be more inconvenient than having your own car, of course, but for the vast majority of people, paying $200 a month instead of $800 a month for a car payment/insurance/gas is more than worth the difference in convenience. With the algorithms, you'll have a car ready every time you need to go to work, or home from work, etc.
If you can actually make it that cheap, it might be the majority of people who live in areas that can practically be served by such a service. That still leaves out almost a third of the country, though.