Higuain several years ago was one of the best forwards in the world, definitely in the top 5. Dybala was considered Messi's heir and that was for a reason; even though he had quite a bad season, he's got an incredible talent.
Both these players seemed lost and lacked motivation last year. But now both of them seem highly motivated and determined to play for this team in the coming season. That's the best type of mindsets the club can ask for.
It would be wrong to sell any of them in these circumstances. Mandzukic to Man Utd - ok, I'm even kind of excited to see him in EPL, because he will show them something, that's for sure. Kean to Everton - not great, not terrible.
But don't sell Dybala and Higuain. Let them prove what they want to prove.