Was wondering if an epic sword that's broken once, can be broken a second time. Google/reddit results were inconclusive, so thought of trying it out anyway. And it did - on my second try an Olog broke my Amaranthine which was lvl 83, is now lvl 90. I think that's the max.
The Amaranthine is the next best sword I have to the Humiliator due to the might gain.Will to try upgrading the Humiliator next
Disclaimer: The chances of an Olog breaking a sword is rare, so there is no guarantee it will happen on the first or second tries, but keep at it.
Video on how to achieve a Broken sword
Hope this helps.