I don't really remember, but didn't they just say it was lost and not destroyed? I'm only like 20% sure. lol. I read the book, but it's been a few months.
Uh...the new books conclude with an ending that makes it clear that if Umbra were to appear, the events of what happened would be greatly diminished.
My opinion, [censored] Umbra. A sword made out of nothing more than noob drool.
Seriously, if you haven't read Lord of Souls yet, just know that Umbra shouldn't appear.