Well, unless Bitcoin somehow retains its value after the attack (in which case he could just steal, steal, steal), he would either have to be smart enough to be able to end up with other assets/products/currency that don't lose their value, and also get away with that (staying anonymous or within the bounds of the law somehow). Or he would have to take a large enough short position to cover the loss from the crash of Bitcoin, which would probably also be quite a tall order, as far as I know.

But rather than taking a large short position, he could also invest in ETH instead, and hope that a fall of PoW will elevate Ethereum by a large enough factor to cover his costs (and future loss of revenue from his ASICs).

Now, the thing about this latter option is that if it succeeds, it will also make all other Ethereum investors besides him have their ETH grow in value by a similar factor. So by e.g. creating a smart contract like the one described in my preprint, he might be able to get some of these other Ethereum investors to help fund the attack, thus lowering his own costs and risk associated with it.

If enough Ethereum investors joins in, the risk of losing $6B–$16B might be worth the potential gains (of upwards of a trillion dollars) if the plan succeeds.

But yeah, not saying that investing in ETH is the only option (let alone paying the miners in ETH).