Firstly, if indeed a dead spren/shardblade can be resurrected, it will be an entirely new thing. However, we know already that it is technically possible to do. Syl came back, but it was Kaladin who returned to his Oaths. The Radiant is dead and cannot do so now. So how would this happen? The Stormfather is not exactly a flexible being, and Tanavast was never much good at seeing into the future. Thoughts/theories that He wouldn't have thought of yet?
Second, the man "broke his oath to kill