This is as close to a walk-off homer as you’re going to see in football. I acknowledge that field goals and touchdowns, i.e., scoring to win games, is in that way more akin to homering to win games. But those are usually resolutions to developing situations. A walk-off sack, like a walk-off homer, is rather a relatively unexpected event, something that ends that game in the sort of exhilarating, out of the blue manner that a field goal lacks.
In that vein, a walk-off pick six is more like a walk-off sack than a walk-off field goal.