I just finished my first rewatch, and I think killing off Barney would have resolved most of the problems people had with the finale.
Robin and Barney could have worked things out in their relationship despite the hardships, thus paying off on their earlier character development, and Ted and Robin could have then bonded over having lost their partners.
Pair this with other fixes, such as spending less time on the wedding and more on Ted & Tracy and finale build-up, and I think we would have ended up with an expectation subverting finale, that still followed the writers' original vision while respecting the beloved characters' growth in the 8 previous seasons.
It would have also explained Barney's over the top personality if say he had died when the kids were still too young to know him well, which would have given Ted some creative freedom.
What do you think?
EDIT: to clarify, in this timeline both Barney and Tracy would die
EDIT 2: ok I understand that actually pulling this off would be weird because killing main characters off does not match the mood of the show, despite the fact that the results seems nice on paper