If MSD rests again tomorrow, I hope Faf takes over the captaincy instead of Raina and slots into the XI. Faf is a better leader and he would also be a better fit for a sluggish Chepauk track. A break (rest) can be given to Watson so that he can be fresh and ready for the playoffs. My XI for CSK tomorrow (if MSD does not play) would be this
Faf (c)
Vijay
Raina
Rayudu (wk)
Jadhav
Bravo
Jadeja/Santner
Chahar
Harbhajan
Tahir
Mohit
If MSD returns for tomorrow's game, I would have MSD in for Jadhav with MSD taking over captaincy and keeping duties. Mohit is a good option on Chepauk's slow wicket. And we've had games in this IPL before where CSK have fielded only 3 overseas players and so its not a necessity to play Santner or Watson forcibly (unless Jadeja's illness continues, in which case Santner plays for Jaddu).
Need a win tomorrow against Delhi to consolidate position in the Top 2. Same for Delhi too. Tomorrow's clash is a fight for the "Top 2". With MI having a chance to enter Top 2 if they win both their remaining games, CSK and DC will be on their toes tomorrow to get their spot in the Top 2. This is where CSK need to use home advantage as DC's team is built for wickets where the ball comes onto the bat and Chepauk has been super sluggish this season for the most part.