I have two large windows in my front room and kitchen. I used vertical blinds, not horizontal blinds on these two windows…along with sheer curtains, drapes and a valance. When one of the vanes breaks I repair it using a three-hole punch, because I do not own a single-hole punch.
Turn broken vane upside down.
Punch a hole in the center of the bottom edge.
Re-install upside down.
Put a piece of packing tape on the back of it at the top for reinforcement.
The broken part is so close to the floor that it is not noticeable.