Chelsea have decided on what to do in regards to Sancho and they have decided not to sign him on permanent basis and will pay Manchester United 5m because they will be going against the initial agreement. Sancho will have to look for a club at the end of the season, I believe Manchester United will be willing to sell.
Sancho's performance is not up to Chelsea's expectations, so returning him to United and paying a fine is not a problem. Although it is a loss, it is better than buying him, but his performance is not good enough next season. This season he played 30 times, scored 3 goals and 4 assists. Chelsea should expect more players than that for next season's competition, especially if they succeed in qualifying for the Champions League. Of course, they expect players with better performance.