If you look at several previous posts, Antonio Conte will not be worried about Osimhen's departure because there is still Kvaratskhelia who the new coach can rely on and there is no need to hunt for new players who have the same reliability as Osimhen.
As far as I know, Napoli is trying to keep one of the players at least. But it is untrue if Conte isn't worried because Osimhen and Kvaratskhelia actually have different positions in the lineup. So if one of them leave the team, Conte must sign a new player to replace the position left by the player. It is not easy to get a new player who has the same level as them. And it should take a lot of money to sign a top player, Napoli must do a hard effort if they must sign a player with the same level as Osimhen or Kvaratskhelia. Personally, I hope both of them will stay in Napoli.
Khvicha Kvaratskhelia and Victor Oshimen are both strikers so Conte can still rely on one of them if it is true that one of them will leave, in my opinion Oshimen and Kvaratskhelia's performance is not much different and Conte can put Kvarat in Oshimen's position but yes Conte still needs players others to fill the void that will be left behind.
It is the hope of Napoli fans that they don't want to lose one of them because they are an important part of the club, but if one of them is uncomfortable leaving is the best decision rather than forcing themselves.
Talking about the value of Osimhen's clause, there is new news that Osimhen still wants to leave Napoli and with a clause value of around 120 million and PSG could pay him, but reading this source I think that Osimhen seems more interested in accepting offers from premier league clubs.
The latest news I know, Napoli wants €150m for Osimhen. PSG already made an offer above €120m but it was rejected by Napoli management. I don't think there is an EPL team that wants to pay for €150m. I guess only PSG which is very serious to sign Osimhen and they want to spend money over €120m.
Whatever the price, it is clear that Victor Oshimen is an expensive player and only rich clubs can recruit this player, not only PSG dares to make an offer to this player. The Premier League is also occupied by rich clubs and I see that Manchester United is also interested in this player, but they had to sell one of its mainstay players to be able to recruit Oshimen. Let's see which of them can finally recruit Oshimen.

Source :
https://www.bolasport.com/read/314114003Just as you rightfully pointed out, victor osimhen is definitely going to be an expensive acquisition to any club that want to got his signature on paper, because he is not just and expensive player, but also a very top players also, and it's only few teams that can afford him, though I disagree on what you said that it's only psg that would be able to afford him now, no, Manchester united can afford him if they want to chase this particular deal, it's just a matter of if they are willing to chase this deal.
But to me, on a career move for victor osimhen, I would have love it if he stay put at Napoli, if no English team is able to acquire his signature, than going to Paris, because as for me, staying back at Napoli is not a bad move either, because since their new manager is Antonio conte, they are more likely to challenge for trophies this season, so moving away from the club should not be a must, to have a successful career.