RMQ deals with this fairly decently now via flow control (as of 2.8.0, I think). Basically, if it determines that the queue isn't keeping up with publishers, it'll throttle publishers (by blocking on publishes) to slow down publication to a manageable speed. It also uses this mechanism to block publishers if free memory/free disk space fall below preconfigured thresholds. When a publisher is blocked, RMQ notifies it that is has been flow controlled, so the publisher can optionally take some action to help mitigate whatever circumstances caused the flow control.

It's not perfect, but it's actually pretty good at mitigating the problem of RMQ causing an RMQ-oriented system to eat itself.