Not likely to go extinct that quickly
a. Extinction - unlikely in 100 years.
b. Perfect sustainability - unlikely without a world government controlling reproduction - right to lifers would never approve it.
c. Cyclical growth & die back - most likely. A lot depends on how many other species are driven into decline and extinction. Our best bet is to encourage as many species to survive and thrive with as little intervention as possible. High maintenance species, unless they are a keystone/linch pin species, are a waste of resources. Our best strategy is actually re-forestation with a variety of different trees and shrubs - not mono-block replacement a la factory farming principles.
d. We expand into space and begin using the resources there - not going to happen. Governments are what prevent our rapid ascent into space. They are terrified of anyone with the high ground and the ability to drop any improvised kinetic energy weapons on them; much less atomic powered space craft. Until we clear away the horrible mass of restrictions, only the most wealthy will every achieve orbit.
