Chelsea have to hope their youth policy finally pays of now, after 10-15 years of investment in young players it needs to produce. With Roman tightening the purse strings and the transfer market becoming silly, the only way Chelsea can compete is to develop these players into stars. They could have done that with De Bruyne, Lukaku and had decent/good back-up players in Romeu, Ake, Chabaloah. I'm probably missing a few that could get into their team.
Christensen has been a big plus point for them this season, Hazard, Courtois and Kante are top class but apart from that their team is weak. It's too early to say how Morata will fare long-term but the jury is out. They need to bring through players who can have a similar impact as Christensen saving them thousands in the transfer market while keeping them competitive. Musounda, Mount, Loftus-Cheek, Boga, Hudson-Odoi, Abraham etc.