If Tether is a fraud (likely), it appears to be a simple one that's rather difficult to implode. Because of their widespread use in trading and limitations on fiat trading / capital controls around the world, it would be a challenge to start a run they couldn't cover by just honoring redemption requests. If they only held 10% it could happen, but if it's ~70% as often claimed, I don't see it happening.

I'm not sure what could collapse Tether other than Tether itself saying they're broke and refusing to honor redemptions.