Where's the crack? Show a close-up picture. the hairline crack may be just in the paint from the theft attempt. Pick off the paint in that area and see if the metal is cracked as well. One of the benefits of 7005 aluminium is it can be welded without needing post-weld heat-treatment like 6061.

As for the bike, it's definitely salvageable, depending upon how much work you do yourself. A complete overhaul is all it needs, about $100-200 in parts and $200-500 in labour at a shoppe. Comes down to whether you can buy another bike in comparable post-repaired condition for a similar outlay.