Apologies if this has been mentioned already; I'm just catching up on some emails.
But if the top tube and downtube need to be replaced, you could consider having S&S couplers added while you're at it. If you want to retrofit an existing frame with couplers, those tubes have to be replaced anyway. If you're attached to the bike and it's of any use to you to be able to pack the bike in a smaller case, having it coupled would be a way of justifying the repair. And it's cheaper than a new frame with couplers. I fly with a bike at least once or twice a year anyway, and if I busted those tubes but everything else was okay, that's probably what I'd do.
And I always fantasize about a bike trailer that can double as a flight case, so you can ride to the airport with your suitcase in it, pack up the bike when you get there, check everything through, and then unpack and ride away from thei airport at the other end. I know Bike Friday makes such a thing, but you could probably design that around a case for an S&S coupled full sized frame, too.
Emily O'Brien
Medford, MA