The suburbs will maintain their own roads before the bottom falls out. low income suburbs probably will not survive, but there's no law that says they cant have shitty roads that require a jeep to drive on
If a suburb can attract some retail or office space or manufacturing, they can be like Irvine or Tysons or Bloomington -- the suburbs that have made it. Those that cannot will accumulate the same problems with fiscal sustainability that inner cities once did.