"Night gathers, and now my watch begins.
It shall not end until my death.
I shall take no wife, hold no lands, father no children.
I shall wear no crowns and win no glory.
I shall live and die at my post.
I am the sword in the darkness.
I am the watcher on the walls.
I am the shield that guards the realms of men.
I pledge my life and honor to the Night's Watch,
for this night and all the nights to come."
After everything is over,I imagine House Mormont to be the warden of the North.Starks are gone,Targaryens are gone...So Mormonts left Bear Island,rebuild a castle from the remains of Winterfell.And they ruled with justice and lucidity.
Many years later,when everything is in order Ser Jorah knew it's time to hand over his sovereignty and join the Night's Watch.His foster child little Sam cried like a baby when Jorah told him his decision.
Following his father's footsteps Ser Jorah Mormont head to the North.Where it's tought grumkins and snarks are lurking in shadows in days of yore.