Sting was a part of the 2K video game launch events over the Summerslam 2014 weekend in Los Angeles.
Sting was lobbying for a match at Wrestlemania 31, which he would consider a one time WWE match as his last career match. His focus was on a match against the Undertaker. Since he was saying it publicly as part of a WWE event, it’s assumed that it’s in the realm of possibility and he’d discussed it internally. It’s mostly whether the Undertaker is physically able and willing to do another match.
While he hasn’t officially signed, all signs point to that happening in the near future. Sting was recently flown to Stanford, Connecticut where he met with Vince McMahon face to face. While they might have met in passing, it’s the first time they have met face to face, despite having negotiated by phone over the years. He was shown around to tons of employees and shown how the operation works and they generally don’t do that unless they are fairly certain a deal is imminent.