Amqp brokers have persistence settings that allow guaranteed delivery - but that only works if the message actually reaches the broker. If there is a network failure and a subsequent client crash/reboot messages could be lost. Is there some way in rabbitmq or activemq or some other messaging framework for the client (producer) to persist messages to disk so that in the event the client crashes or is rebooted any unsent messages will not be lost?
I have seen people run a broker locally in order to get around this issue. That seems like an unnecessary amount of work, especially if you don't have much control over the deployment of your client.
In reality you've answered your own question pretty well. Many people looking for client side persistence turn to embedded brokers because it's actually a very good solution. Having a local broker that can store and forward gives you a lot more flexibility than just an built in persistence layer in each client, all local clients can share one broker instance which can allow you to move storage as needed in cases where you find that your stored local messages are building up due to unforeseen remote downtime.
There are of course some client implementations that do offer storage but finding one depends on your chosen broker / protocol and of course your willingness to shell out the money to buy support or licensing if that client happens to not be from say an open source implementation. The MQTT Paho client does I think have a local storage option as do some others.