I don’t understand why this would be the “end of the dollar”. It would reduce the need for the dollar to a degree but anyone wanting to buy or sell from the US would have to convert euros into dollars or dollars into euros as the case may be. It those situations, it would increase the currency transaction costs but have little additional effect.
Being the world reserve currency soaks up dollars, which dents the inflationary effect of deficit spending and Fed expansions.
Bush started the stripmining of that privilege, Obama is worse by 10x.
It’s because all of those petrodollars in circulation will no longer be needed and the marketplace will be flooded with the excess dollars. It’s a supply/demand thing. Dollars will still likely have some value, but their value will be greatly reduced because of an overabundance of dollars in the world (since petro transactions will no longer soak up a ton of the supply).