Chelsea can still sign him if they are so serious about it. Obviously, they would have to offer him a lot of wages and also make sure they qualify for next season's Champion's league tournament.
I am sure Chelsea is very serious to sign him. But I doubt if Chelsea wants to spend a lot of money. Real Madrid is a big club that has no problem with money. They are brave to pay a big money to sign a player as long as he deserves. Bellingham is the most potential player in Dortmund, his current market price is €90.00m. But I think Dortmund will ask for more €100.00m.
Real Madrid currently has a very packed midfield, and I feel a player like Bellingham may be hesitant to go there because of the likelihood of ending up warming the bench.
Bellingham will replace Modric who is 37 years old now. He must be guaranteed to be the main players in Real Madrid.