I was recently in an accident and just aft of the weld where one of my chainstays meets the bottom bracket (actually on the Lite it's the motor assembly) cracked, but not all the way through. I've always been under the impression that once an Al frame is cracked it's dead, but one of my neighbors is an industrial welder, and works with Al daily, swears up and down he can repair my frame. His says he can re-weld, and then sheath my chainstay.
Is this a reasonable fix, or would I be taking my life in my own hands?
I would personally get a new frame (and its a new excuse to get one) but even if you do go the repair route (dont recommend it), if you re-crack the stay, the wheel will probably cock to the side and start rubbing on the opposite stay.
This type of crack is usually from the design of the rear stays more than any tumble.
Having no bracing the rear movement under load works the stay and weld until one of them cracks.
You can repair it with a weld and some reinforcing (sheath's good) if its a thin tube and also get the welder to plonk in a brace somewhere between the rear wheel and the bottom bracket to increase rigidity.
I'll take it as given you have the equipment to align the frame for this job, keep in mind that any misalignment on a Giant may not be from the tumble.