Two questions:
1) How long you think Minato will stay? I wonder if Orochimaru will give him time to stay for a bit.
2) Joke or not but does it really feel like Minato is a plot shield for NS? To be honest, as funny as it sounds, I admit that's a bit true. I mean I feel like other pairings are on halt minus NS because one false advertisement and he'll be like "Oh you're a liar." I can't see it. So yeah, thoughts.
1) If Orochimaru assists Sasuke with whatever he plans on doing, he might leave sooner or Orochimaru may try to control him. Maybe Hashirama can keep him from doing it, after all he wants to be careful with him lol. XD I agree that Minato will leave when Obito dies, that would be a nice closure for him. I also think it would be better for him to just fade into the afterlife instead of being sealed. :')
2) As a part of the audience, 631 is a humourus context. But as far as the characters are concerned, it's dead serious. It's only meant to be funny to us, no laughs or chuckles from their side. Of course Minato would accept any lover of Naruto, but he can't get away without any scolding now because it's hard to take back something that serious. If that was the case, Naruto should've said it right after the so called "joke". Meaning that if a NH moment is coming, Minato is bound to at least be confused. NH would only be drama right now, lol. 