As noted, John Cena recently suffered a rotator cuff injury and will have to undergo surgery to repair. This injury will keep Cena out for 6-9 months. Cena was expected to be a major part of WrestleMania 32.
Dave Meltzer said on the most recent episode of Wrestling Observer Radio that WWE is changing plans again for WrestleMania 32 due to Cena's injury. Keep in mind that one year ago, Vince McMahon had matches already booked for the event but plans had been scrapped due to Seth Rollins' injury and because they found out that Ronda Rousely would not be available for the show. Plans also changed when McMahon decided to end the Undertaker-Brock Lesnar feud in October. Cena was rumored to be facing The Undertaker but that is obviously not happening.
WrestleMania 32 will take place on April 3, 2016, at AT&T Stadium in Arlington, Texas.