Long before that he basically took a wife. Sam's a nice guy with many virtues, but fealty to the Oath has not been among them.
I know at least one Wikis says the Watch disbanded. But was this ever formally done? And even if it was, I don't think that should absolve the men of their oaths. The Oath says their watch does not end until their death. Not when the Wall falls, not when the Night King is defeated. And not even if the organization falls apart. I don't see how the Oath does not stand, and if the showrunners and GRRM disagree with me, then to hell with them.
I don't see how they are released without an act of the King or Queen, or religious act, or something like that. And though I can certainly imagine some might just decide EFF it, the world has changed and the oath no longer applies, I cannot imagine that being unanimous, and there would be fights over it.
Hell, that the Wall has fallen makes their duties more important, not less. As for defeating the walker invasion, the Watch was founded -- and the wall was built -- after they just beat back a prior invasion. So even if they win this there's no reason to think there won't be another in a thousand years or whatever. Maybe they achieve some sort of total unambiguous victory but that's getting ahead of ourselves, and with magic and such anyway how they could possibly know for certain? Is someone going up North to conduct a thorough census and check if the walkers left behind a remnant? Even if they did not unless the Children of the Forest also are dead then the threat is not gone. If the Children live (and I don't see their extermination as either a goal or a likely outcome), then nothing is completely over.
