Hey mate, I had a similar situation...I've dismantled the legendary sword a few weeks ago, simple because I didn't like it plus I actually needed a few marks to buy smth, anyway I've dismantled it before I found out about the exotic sword quest...was pretty pathetic and shame on me for that but manned up and deleted one of my fully upgraded warlock and started a new one, because that's the only way to get another legendary sword etc. In fact you can use a spark light which puts your fresh character on lvl 25 straight away.... After that you do the entire ttk story line, what takes a couple of hours. Once you complete it you'll be about 36 light lvl and then you can do some old story lines on heroic to get quick xp plus do some bounties as well. I only took me 4.5 hours to reach level 40 and one of my subclasses was fully upgraded. And yeah just before you delete your character make sure that you put all your good gear in to the vault and only leave uncommon or rare gear equipped. You're welcome