The way to save Yahoo is for Yahoo to kill Yahoo.
Tumblr is in New York. Away from Sunnyvale. Yahoo could build a new Yahoo there that was comprised of small teams, making new products, shipping on a regular cadence, shielded from the mothership.
When the original Macintosh was created, the team was in a new building away from the Apple II team. Yahoo needs to find its own pirate flag to fly.