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", that she's secretly loved Vlad for years. When I say all this was contrived by the Cycle, I don't mean that the Cycle has a mind and a plan, but rather the Cycle is a force like destiny, or karma: what must be, will be.
2. In the next book, armed with a Great Weapon, aided by the ability of the Phoenix Stones to keep his movements secret from the Jhereg Council and its assassins, Vlad will return to take on the business end of House Jhereg. In many ways Vlad is a nightmare both for an assassin trying to assassinate him and for the Jhereg council. He's an assassin himself, alert for every trick and strategy for eliminating a target, which he now is. Because he can't be tracked, he can't be surprised in his sleep, nor can he be ambushed, as he'll be too smart to have any kind of routines or patterns that will make him easy prey. Too, Vlad yields a Morganti weapon, so any assassin already committed to kill Vlad now has the added stress of knowing any mistake in killing Vlad instantly will most likely cost him his soul - and then there's the unnerving effect of a Morganti weapon on the assassin's mind, making a mistake more likely.
I suspect after one or two assassination attempts Vlad will decide to hunt the hunters and make it his mission to destroy the Jhereg Council and after some hair-raising adventures will succeed at assassinating one or two members on the Council after which the remainder of the Jhereg Council, led by the Demon, will negotiate with Vlad, offering him a seat on the Council in return for him calling off his one-man war against them.