He suffered from an ACL and a MCL injury which means he's out for 6-9 months but what is impressive is that even after suffering the injury, he managed to powerbomb a 320 pound guy and finish the match he was in. Seth Rollins by no means has had the best title run but that's not entirely his fault however, when he was in the ring, you know he was going to put in a good performance.
As of now, it's unclear what will happen to the vacated title. Most outlet suggest that a tournament will be held at survivor series and with the winner being crowned the champion which leads people to believing that Reigns will win the championship at the end of the night. Another theory is that Sheamus will cash in at the end of this tournament to pin Reigns (which I hope doesn't happen since Sheamus is unbearable). People also seem to think Dean Ambrose will turn heel during the PPV to cost Reigns his shot since it's been speculated that Ambrose's character will be turning bad for the past month or two.
It's also worth considering that there have been a few rumblings that WWE will call upon a "big" star to hold the title but there aren't that many available at this time. They could also throw Lesnar some money in order to have him do more dates and hold the title which is a reasonable outcome since he's coming off strong from his HIAC match with 'Taker. In light of this event of Rollins' injury, this PPV may turn out to be better than expected, a silver lining if you will, with this being such an unknown element as to who will come out champ and brings genuine unpredictability to the product if they play it right.
As for Rollins himself, this might do him good as well since it's been long rumoured that he was due to turn face and now being shelved for the good part of 2016 (until post-wrestlemania) he could return around Summerslam time as a Face, get a huge pop upon his return (à la Triple H 2002) and go from strength-to-strength.