If Rollins loses at Battleground, look for Raw to create a new championship title for Rollins to acquire. He is the most popular wrestler on both brands and you can expect Raw to push him constantly into the spotlight. Either Rollins will be hunting a title or defending one. I doubt the writers will put him in a tag team competition, so a singles title is the path for him.
There are only 3 wrestlers in Raw that I can see Rollins realistically having feuds with in title competition. Roman Reigns would be a good matchup. The two men have history together as members of The Shield. Brock Lesner, who is fresh off of a UFC controversy for apparent drug allegations. Lesner isn’t returning to the octagon anytime soon, so look for him to stay in the WWE. Lastly, Finn Bálor who is a fan favorite from NXT. Bálor will be champion sooner rather than later, and Rollins would be a great opponent to baptize him into Raw.