I don't think there really are any (or many) reserves. I think they just printed a bunch of tokens, used the tokens to buy BTC and to inflate the value of the crypto they hold in Bitfinex (Bitfinex and Tether are approximately the same company). If they throw in the towel they lose their ability to influence the crypto market which is where their actual gains come from.

Jail or death. They’re rumoured to be heavily involved with drug cartels for money laundering.

But jail is a near certain outcome if they just took the money and ran off.

So they’re stuck with it. Once it implodes they’ll also face jail, but they can kick the can down the road.

If we're being totally honest, the incentive not to do so is probably death. Who knows who is "invested" with them, doubtful it's people who like investments with accurate record-keeping.

Can they even do that? What would that actually look like, from a technical perspective?