I've never gotten a straight answer if the downer ending is available anywhere, but I'd like to see that too. It's somewhat of a downer ending as is, but w/ the one where Cord gets gunned down, we're talking The Great Silence territory. In my rating, it'd definitely go up a point w/ the downer ending. 
The german version is even shorter with only 94 min, but it has the downbeat ending.
Cord is shot by the 2 bounty hunters, who had appeared earlier in the movie, just when he has left the town. One says that it was never so easy to earn 10.000 bucks, but then they find the amnesty paper and he begins to laugh like crazy.
In the 118 min version this could become a minor classic.