This is not quite correct. The liability is hidden, but it exists — it’s the requirement on the network overall to continue mining and validating transactions.

If the network stops for whatever reason, the instrument is unusable and valueless. And the cost of continuing to run the network is borne by miners, more active traders, buyers and sellers. This cost is the cost of security, and for proof-of-work systems, it is very high.

Edit: I’ve now written this up more extensively. And the reason it’s a liability isn’t because the blockchain can fail — it’s a result. https://medium.com/@davidmanheim/blockchains-reserve-banks-and-accounting-for-liabilities-1fbbc39b5f4a