I do not think the ASO would take the step of awarding the TdF titles to no one. They never have and it's highly doubtful they ever will. That said, ideally is that what the ASO should do? Honestly I don't know.
We have some experience with that here in the US with pro baseball. It came out that for a number of years many of the top players were pumped up on steroids. They ended up choosing not to strip the records set, games won, etc. The problem was so widespread that it would have been very difficult to do so in a fair manner. I suppose the other alternative was to wipe those years completely from the books. To no one's surprise, that didn't happen.
As for Landis and Contador, I think you're missing a key part of my point. Did those yellow jerseys go to riders proven to have been doping? No. (Yes, I'm aware that there were allegations against Pereiro w/r to an asthma medication. They were investigated and his explanation was accepted.) That makes the situation quite different than handing Jan Ullrich three more yellow jerseys or awarding one of Armstrong's wins to Ivan Basso.
To the comment from another poster that the USADA doesn't care happens with the TdF titles... all they care about is pursuing the case against Armstrong... okay, that's fine. But pro cycling does care. If the USADA is successful in proving their case, the ASO and others have to decide what to do on their end. Do they pass the titles from one doper to another? Do they declare that no one won? Neither option is good, IMO.
On a side note, maybe this investigation will convince Radioshack to fire Bruyneel. They should do that for his incompetence this season anyway.