I am a staunch supporter of both Barcelona FC and Argentina national team which I've been a follower since the 90s. In fact, I have a very faint memory of Maradona winning the WC back in 86. My point is I've seen the evolution of Argentina team. I've seen them win and lose in all the WCs. But ever since Messi donned the jersey of Argentina, he has taken them to the next level, giving the belief of holding the golden cup again, and starting a new era for the Argentinians. In comparison to all the previous WCs and cup matches, now I see a Messi who's no zeal to get to the finals of the WC and winning the cup. He's nervous, confused, scared and at times even tired (mentally). It would be hard for Messi to come back to the Messi who was in the 2014's WC where he had a mission to achieve, but still, I am not writing this team off. With inspired Messi, they can still achieve the unthinkable. I still believe that Messi and the team can qualify and reach the finals, and with luck and good play, they can win the cup.
And for the tactics, I'd say Sampaoli must use whatever he has best to play against Nigeria. And who says Messi can't play with Dybala! As a matter of fact, Dybala can help Messi by attracting players and freeing up Messi.