Not to mention all the derivatives of Oil which people never think of, like Plastics, Rubber, Solvents, and so on.
There are alternatives, but cheap access to oil is the basis of our global economy and without it we would see global unrest and societal collapse. (if we assume a rapid loss, rather than the more realistic gradual move away from oil products beginning with the more viable and economic alternatives)
However, as the interregnum subsides (due to population decline and the isolation of communities) I expect we would see a new and hopefully more responsible civilisation rise up.
What alternatives?
I really do suspect it would descend into war personally in this scenario, 'end game' style thinking at least, not necessarily mass killings or military confrontations however.
If any state still has a calculated amount of oil product reserve and military power left, and you know you can still dominate the declining world perhaps in the same manner you did in growth, you could see an emergance on a potential world
unification under one sovereign banner. Or certainly true Orwellian bloc powers if not. Imagine it being America or Russia by default at present.
Why would they do that? Well, I'd hazard a guess at humanity not really learning any lessons, and probably blaming each other by this point for the collective failure to progress.
If you can get increadibly more technologically advanced than any rivals before this potential long term major setback, it gives you time to let the rot set everywhere in order to make your sunset interjections easier.
Sit back, recover. Watch the sun rise on a glorious new empire that was snatched in possibly the easiest way possible.
Of course, this all has a set back. Nuclear armament.
I'm not sure if MAD would scale back with the decline, in terms of principle and quantity, so until I can figure that out with certainty my world domination plans have to stay in my shirt pocket.
Could obviously go good or bad.
Perhaps I was too taken with mad max as a kid, but I can't help but feel in times of true crisis you tend to see more of the underside of human nature than the better side.