So. Did we just exchange Rhuobhe the Awnshegh for Braedonnal Tuare the Awnshegh?
That's always the problem with these little endeavors. Birthright is a rather evilly clever setting, that way.
Hard to say what really happend. Bjorn is quite ambiguous here (as in most times). I can imagine several variants:
1) The "smoked too much" Trelien has an hallucination before his collapse and things happend quite diffrently.
2) The fight of Rhuobhe and Tuare really occured, but Trelien in all that smoke and his bad state have mistaken Rhuobhe for Tuare and other way around (after all both are elves and they are for human notoriously hard to recognize ono from another), so it was really Tuare, that fell.
3) Well, it really happened as Trelien saw. Having opportunity, one of Rhuobhe's own killed him from behind. Probably they just had enough of him and wanted something different. Then
a) Tuare has "become" Rhuobhe and said "Don't worry, Im your old leader, even when I look different. Lets continue in
ghaellie sidhe"
b) Tuare has finally resolved his personal differences with Rhuobhe and since he allways hated humans as much as Rhuobhe, he has taken over his position after his death with words "Now you will follow me.
Ghaellie sidhe will continue till humans are extinct."
c) Differences between Rhuobhe and Tuare were political. Otherwise, they were close friends. After Rhuobhe's death, Tuare said to elves "Your leader is dead, this his sword will never strike again.
Ghaellie sidhe is over. Find something better to do."
And yes, don't forget no human really knows that this has happened, unless Trelien makes it back from the forest (which I strongly doubt). For all we know, Tuare perished with the rest of the losing side and Rhuobhe is still there and still pissed off.