I know that usually you have to pick one or the other. But, what if I use "Last wish" runeword and the Fade kicks in with the ctc. Will I have both BoS and Fade at the same time?
Doesn't matter where it comes from, charges, items or the skill itself: you can't have BoS and Fade active at the same time. If you trigger Fade with 'Last Wish', it will override the BoS you have active.