Right up until the final moments, Telumë still doesn't know if it's going to work.
But he stands on the dusty road in Velvar, facing Sauron, dizzy and drained and exhausted, heartsick and numb at the same time. Too many deaths, too fast too soon they weren't ready - too much he had already lost, long before this final battle, too much that can't ever be set right even after they win. If they win.
But Vanyel is with him, and he doesn't hesitate.