Renewables

[Drashner1]

Decades are a fairly trivial amount of time, actually. And your description here leaves out the options of the rising cost of non-renewables making renewables more competitive, new technology making renewables more competitive, continued construction of new renewable sources picking up the slack, increased use of telecommunications tech making travel less necessary, construction of nuclear sources coming to be seen as more acceptable if the alternative is societal breakdown, development of more efficient tech to reduce demand while maintaining the 'industrial' standard of living, development of better recycling technology, and location and extraction of currently unused sources that may become either more competitive or simply seen as necessary for civilization to continue - the main of this last would be mining of methane clathrates from the ocean floor. To date this last is seen as too risky, but given the choice of that or civilization collapse, someone somewhere is likely going to try it (not a preferred solution but a possibly attempted solution nonetheless. Probably other options as well, but the above are just a quick overview off the top of my head.

The issue that is being missed here is that people are not likely to simply sit around doing nothing until a bell rings and then civilization collapses. Instead, as oil becomes less available, other options become more competitive, people are driven to try new things. societies adapt, new technologies are developed, and what was an unacceptably high cost before suddenly seems like a much better deal.

All of these and other factors together have the effect of extending the remaining resources and allowing more time for further changes and solutions to be implemented. While not as dramatic (and perhaps not as satisfying) as a great global coordinated effort, it's been in play for a while now and can get the job done.

I'm not sure what you mean by 'preserve what we can for future civilizations'.