"For a Brit who doesn't understand the complexities of US voting,
can I now go to bed confident this is a definite indisputable conclusive victory ?"

Yes, this was a conclusive victory for democracy, not just for Dems and Obama.
The American voter overroad the cheating and conniving of the GOP sometimes
standing in line for 6 hours to honor their franchise.

This was a victory for the people of the United States.