I don't think it's obvious that Hazard and Courtois want to leave. In fact, I think they'll both stay and sign new contracts. Hazard has said since April that he wants to stay but the club need to refresh the squad with new players. Yes, he used the world cup as a convenient excuse to not get drawn into contract talks but I think once the dust on the world cup has settled and he has met with Sarri and Zola, he'll sign a new contract before the end of August.
I think Willian's problem was with Conte, and with Conte out, I think Willian has no reason to be upset anymore. That said, I think most Chelsea would gladly see sell him to Barcelona tomorrow. Jorginho is another quality midfielder to the ONE we already have, so let's not pretend he isn't a massive improvement to our midfield - we had Bakayoko, Cesc and Drinkwater shuffling about next to Kante last season.
I do generally agree that we need couple of more signings on top of Jorginho. Apparently Golovin is close to happening, we have been sporadically linked with Martial and Bailey, both would walk into our first 11.