After reading Issola, I came to two conclusions: 1. All the events were orchestrated by The Cycle for the purpose of bringing together all the parts and players required to create the Great Weapon (Godslayer/Lady Teldra). If the events described in Issola had not occured, some other set of circumstances would have been contrived by the Cycle in order to bring things to the same conclusion - the joining of a Morganti weapon, a soul & Vlad Taltos into one unit, as described on page 245. It's possible that any other soul would have served as well as Teldra's, but I don't think so. On page 246 Brust clearly states that Blackwand loves Morrolan, Pathfinder loves Aliera, Iceflame loves Sethra, and Lady Teldra loves Vlad and I think we'll find in the next book, when (and if) Lady Teldra "wakes up