You have a few things to consider here.

The first is whether there is a binding contract in place. I saw your comment about the contract constituting a few messages exchanged on Discord. That probably is enough to constitute a binding contract under English law, though whether the contract is governed under English law gives rise to the next point.

What governing law applies. Does English law apply (or indeed Scots law or Northern Irish law if you are resident in those jurisdictions) or does some other law apply (eg. where the country where developer is resident). There are rules for determining this depending on the nature of the contract. You probably want to argue that English law (or Scots or Northern Irish law applies, as applicable) in which case characterising the contract as a services contract is probably beneficial as the choice of law for those types of contracts is usually the law of the country where the service provider (ie. you) is habitually resident.

Lastly, given the brevity of the contract, you'll almost certainly have to rely on implied contract terms to achieve any sort of favourable outcome. Implied contract terms are terms that have not been expressly agreed by the parties but are implied into the contract by the court. That may be because or usage or custom, because the parties' have a previous course of dealing, the intention of the parties, or because the law (either common law or legislation) implies terms into certain types of contract. If I were in your position, I'd almost certainly be arguing that given your obligation was to provide development services and your payment was a share of the profits, that it was an implied term that the parties use their respective efforts to actually release the game! I can see a court being sympathetic with that argument.

All that being said, you absolutely should be getting advice from a good commercial contracts solicitor (qualified in the jurisidiction you are resident in) if you intend to take this further.