Lived and survived on when there was no oil? No theywill not suffer drastically they will either return to focil fuel i.e Coal,or buring more wood. They managed without oil for hudreds od years did they not? No they will not regress to the foot soldier either Unless I misunderstood you the only modern alternative is of course NUCLEAR energy that many countries use it now. And for other usages their is SOLLAR enrgy.Men has adapted ways to find means. Lack of oil will produce the will to enhance their knowledge (21st /22nd century) So,no problem.
Yemeni Shiite rebels to form own Cabinet in 10 days (AP)
from the article: What happens in 50 years when the oil runs out?