If I were him I would reject the job offer.
If he left Juve to achieve higher targets and improve his CV then he shouldnt have taken this job as its a tougher task to win with the NT than to win with Juve and make a proper CL run.
That is not to mention that NT coach performances tend to receive less credit than club performances. Prandelli took the Azzuri to a Euro final and we didnt see the big clubs of the world trying to talk him out of his contract (back then).
Also, I think coaching the Azzuri will diminish the strongest aspects of Conte's coaching methods.. namely motivation and attention to detail. He always struck me as a guy that builds a relationship with his players and motivates the hell of out of them while instructing each player on what to do to the finest detail. With the Azzuri, he'll meet with them every few months before each player goes back to play his role at his club. There is no day-to-day motivation and management.
Moreover, Conte's juve thrived best in the league and suffered the most in knockout games/cups. With the Azzuri its all cups. Finally, the Azzuri squad is arguably inferior to Juve's and at the very best has the same limitations that Juve's squad has.
If the Azzuri job will be good for Conte's CV, Conte will have to win a Euro or a WC.. otherwise it'll be bad for his resume.
If I were him, I'd coach a PSG or City like team first to cement my place amongst the top coaches of today before taking on the Azzurri challenge. That way if I dont win with the Azzuri, I'd go back to coaching top clubs a la Van Gaal as opposed to settling for the Galatasarays of the world like prandelli.
Prandelli's resume ultimately suffered from his role as Azzuri coach because his resume only has a couple of good seasons with fiorentina.