A lot of the artefacts of a process are intended to help teams transition from the old way of doing things and to help teams who have stalled or failed to deliver. Sprints, as far as I understand them, were intended to get the wheels turning and to demonstrate results at regular intervals so the customers for any software development effort could see progress and gain confidence that the team was going to deliver. Once everything is up and running smoothly then it's entirely reasonable to drop all that and just focus on delivering - you don't need a lot of packaging an rituals to do that.