Hope is all we have; so at that moment we will make do with it. But while dense urbanization is better - it is not the only technically feasible solution. Again for the transportation example automated driverless ultra-light rail runs on cheaper tracks with cheaper stations. That lets you put it even in comparatively lightly populated suburbs offering the same convenience the NY subway offers to its more dense population. Known efficiency techniques and known renewable technology could supply our needs and many of our wants now.
And yes if we don't improve our society soon we will lock in even more damage to the planet than we already had. But between nuclear weapons and various other types of ecological destruction, we always knew that one of the many reasons for fight for a decent society was that we were in a race with catastrophe. Now a precipice is in sight; we have a deadline we may not make. But that was always something that was coming as long as the forces of reaction ruled.
Buckminister Fuller, whose life demonstrated that it was possible to be both a genius and a crackpot, once wrote a book titled "Utopia or Oblivion". That title I think came from neither the genius or the crackpot side but from an ability to occasionally see the obvious.