If Chennai loses today and if the tie/rain wash-out happens between Hyderabad and Bangalore, all the 3 teams (Chennai, Hyderabad and Bangalore) will have 15 points. Then net run rate (NRR) is the key for the next 2 teams (other than Delhi and Punjab) to be in the semi-final.
Hyderabad Net RR: 0.265 (this wouldn't change since tie) Bangalore Net RR: -0.253 (this wouldn't change since tie)
Before today's match against Punjab, Chennai has NRR 0.932. RR for 1812/237.5 RR against 1788/242.4
Today Chennai scored 116 in 20 overs. So, new RR for is: (1812 116)/(237.5 20) = 7.487
If Punjab scores 117 in 15 overs, Chennai's RR against will be: (1788 117)/(242.4 15) = 7.401
So, Chennai's NRR will be: 7.487-7.401= 0.086
Still, Chennai and Hyderabad will enter in the semi-finals since Bangalore will still remain at -0.25.