The widely held belief is that Brock Lesnar would be immediately booked into a rematch against Alistair Overeem if he decides to return to UFC. Overeem was the person that defeated him for the heavyweight championship before he decided to retire from MMA and return to WWE.
When Michelle McCool went in for wrist surgery last month, there were speculations that she was healing up for another run with WWE. However, that does not appear to be the case. No such return is currently being planned right now, as she is spending time with her baby daughter.