Questions on DoD and Scrum Masters

Hi all,

I have two questions:

(1) If a product backlog item does not achieve a "done" status at the end of the sprint, what is the best way for the scrum team to address it?

(2) What happens to the SM role in a mature scrum team where all members fully understand and accept the scrum values, events, roles, and artifacts, can effectively take care of impediments or resolve conflicts on their own, and can consistently stick to the time-boxes?

I'm just not sure if these have been answered in previous posts. If so, kindly direct me to them.