Could one live without a car? Yes. I use my GC for probably 85% of our driving here. I could also live without internet & cable tv and Sams and Costco and Trader Joes and Disney and malls but would I want to and would it be CONVENIENT? Not for me. It all depends on your lifestyle and what you like to do "on the spur of the moment." Last week on miserably cold day we decided last minute to leave the bubble. Sure, you can rely on friends, neighbors, car rentals, buses, taxi's & bicycles but it just depends on what you do. Also depends on age. I doubt most folks in the 65-75 - 80 range would want to but if I was 90+ maybe I could.
If you have an older paid off car all you would need to pay is insurance (on an old car you can get cheaper insurance with low coverage) and basic upkeep. Add up taxi, car rental and other transportation costs and you're probably not saving that much. I'd REALLY hate to reply on friends and neighbors because as nice as they are it is still an imposition.
EDit: Just to clarify. If you
never plan on leaving "the bubble" you absolutely DO NOT need a car. If you have to get to one of the non GC accessible local strip malls you can walk across a street or for the rare occassion take a taxi.