My estimated Juventus departures due to age/decreasing level:
2018 - Barzagli (37), Lichtsteiner (34), Dani Alves (34), Mandzukic (32)
2019 - Buffon (41) Khedira (32), Chiellini (35)
2020 - Marchisio (34)
2021 - Higuain (33)
Players who fit between that are basically Bonucci and Asamoah. I'd like to think Bonucci would be here in 2021 and beyond. If he really wants to experience the PL then we will let him go for big money, we've always done that. Would be weird for an Italian but he's a character. Asamoah only has a year left after this season, so obviously if he doesn't renew he's gone in 2018.
Then you've got Dybala - a question of whether he fancies playing for one of the Spanish two. That's probably on a timer but hopefully a long one.
We're going to have to pay the money for a Buffon replacement, we know we have to do that and it will be a marquee signing as and when he decides. Personally I think he'll give Juve another year after WC 2018.
These are the players we have to consider replacing over the next 3 or 4 years. With those who want to leave then you have to directly replace them with quality. Meanwhile we have to look at the quality youngsters like Schick and Conti to compliment guys like Caldara, Rugani, Mandragora, Lirola, Spinazzola, Cassata, Pjaca, Orsolini, Kean and whichever bonus other youngsters come through in that time. We're in a good place to keep our success going for years, it's a good model and eventually those promising players will become the established stars of tomorrow.