I've maintained this is very possible if the AVs are cheaper per mile than car ownership. Long distance road trips could be solved with car rentals.
Average mileage, by typical leases, is 12k miles per year. That's 33 miles per day. Assuming average car payment is $620 a month (averaging new and used averages), which works out to about $20/day. Not even taking insurance into account, that's about $1.65/mile.
As long as AVs can keep rates significantly below $1.65/mile, and wait times low enough to not be inconvenient, I think a good percentage of people in urban and dense suburban areas would switch.