You are assuming no one else would sell them oil. This is incorrect.
The is currently enough oil supply for everyone. Reducing/removing an oil source just means the oil comes from somewhere else, but it does NOT reduce oil consumption.
No, I'm not. But I am assuming that access to the source we're talking about would have an appreciable effect on global supply. This isn't the first time this has happened: the plummet in oil prices in the last few years is in large part attributed to an increase in supply of US oil production. I don't remember the details off the top of my head but I recall reading that the drop in prices has also been accompanied by a halting of the momentum of consumer interest in things like fuel efficiency.
