Imagine for a moment if it were known today that Usain Bolt had 'doped' in the past. The fact alone would set into motion a whole host of nasty lawsuits and financial arrangement crises with people getting fired all over the place - meets cancelled - sponsorship deals crashing, etc... ...If Armstrong can fall, so can others!
I forgot that I also wanted to address this.
The idea of the sport relying on one personality is one of the biggest misconceptions among fans, journalists, officials and marketers in this sport. You even say yourself, Armstrong fell. He was protected by the UCI, probably on behalf of "popularity in the sport" but cycling was still around after he retired and sanctioned. Same with Contador: he was protected by the UCI, probably out of the same idea that the sport "needed" him, but nothing changed during his ban. Rider rode, dopers doped, and the money flowed as it always did.
Bolt hardly competes as it is. Which meets would be cancelled? None. What lawsuits would be filed, and who would fail financially, besides possibly Bolt himself? Nissan? Gatorade? They've survived worse than a sports endorsement embarrassing himself. Gatorade survived Brominated vegetable oil compalints (a petition got 200,000 signatures), and they changed their ingredients as a result. And Nissan's defective radiators and transmissions? Bet you didn't even know about them. Bolt gets caught doping, and... they don't have to spend money on him anymore? They lose faith in TnF and stop investing in athletes? Well, no one else is getting their money.
The sport would keep going.