What if one just cleaned it up and rewelded. Grinding down the original weld some (V-grind the crack if possible). Especially grind a V in the gusset.
It may not bring the frame back to 100%. I wouldn't do competitive cyclocross on it. However, it should be usable for typical city/commuter riding, and certainly could extend the life of the frame for some time.
Personally I have troubles getting a good weld in a deep V between tubes, and that could be a weak spot, although the gussets should help.
On the right side, the crack does deviate from the head tube, but still should be weldable,and still should be within the double butting if the tubes are double butted.