[buzer]

One good option could be to make the distributor (like Steam or Play Store) liable as well. They would then have an interest on making sure that publisher/developer holds up on their side of the deal.

For example they could require that they provided with those EOL patches/sources when game is released, require liability insurance in case of bankruptcy etc.

[account42]

That's an interesting point. Steam likes to pretend they are only facilitating the transaction and the developer/publisher is the real seller when it suits them but I bet that isn't how most players experience the deal.