Cuba fell so far backwards because it relied so heavily on foreign backing that when the money dried up the people were not in a position to afford oil let alone alternatives. This doesnot mean they "wanted" to go through such a change.
A bio diesel EROI of 3:1 suggests that farmers will not have to return to non mechanised agriculture, but conceivably labour may become so cheap in a worst scenario future that it is more profitable to do so.