The response for a flowTriggerReceive mutation request to a shop that does not have any workflows enabled for that trigger is no different than if it did and the request successfully started a workflow.
Additionally, workflows now turn off on the first try even if the app sends an error response to the trigger lifecycle callback (I believe this used to take two tries). And there do not seem to be any trigger lifecycle callback retries.
Which is to say, if your app does not receive (e.g. app downtime) or otherwise unsuccessfully handles the lifecycle callback (and doesn’t have its own retry system in place), it has no way of knowing that a shop no longer has any workflows enabled for that trigger.
In my case, this could be easily solved by sending an error response to the mutation if the shop doesn’t have any workflows enabled for that trigger, which is the behavior I’d expect anyways.