This is the basis of Dimon's prediction: that government will intervene. Perhaps the USA intends to intervene. Perhaps Dimon has heard it intends to do so. Maybe every other country will be pressured to follow suit. Dimon obviously believes this is possible and probable (unless he's talking it down to get in at a better price). Any successful attempt will require some luck. Dimon thinks some aspect of government will make it's own luck.
It won't go to zero because "its a fraud", because it's not a fraud. Even if BTC was a fraud, it can take a long time for frauds to go to zero, based on the history of the USD.
But this is the only reason Bitcoin would go to zero, except maybe for competition within the crypto space. That's not likely as BTC can always adapt when competition gets too keen.
The more likely scenario is the USD is replaced as world reserve by SDR (special drawing rights) out of the IMF. Then Bitcoin will gain value as the USD loses value.