This is a serious problem because they will against Liverpool in the first match. Chelsea actually still have many attackers, including Lukaku and Jakson. But losing one of their best attackers won't be something good. It can weaker their attacking power. However, since there are many other attackers, I assume Chelsea can deal with this problem. Pochettino can consider to replace him with another player or he try an alternative formation.
Well, I don't think it is a problem that they sold Kai Havertz because Havertz doesn't guarantee Cheslea to have a good performance. Chelsea has a big squad, they have many attackers. It is a good idea to sell the unnecessary player if it is needed, especially if they can get a good amount of money by selling the player.
I doubt Nicolas Jackson will he be the striker who will bring Chelsea to change their fortunes this season after failing last season. Previously, Lukaku transfer had also not been completed, even though if it could be completed before the Premier League rolled around, of course Chelsea could play Vlahovic if the deal with Juventus could go smoothly before the PL started.
For Liverpool, they also lost several star players, but I believe that Liverpool are still stronger than Chelsea in the match. Liverpool still have hope for Nunez to be able to show his best quality this season after his first season with Liverpool was unsatisfactory.