5 possible storylines for Roman Reigns when he comes back to WWE 

#3 Pursues the Universal Championship

His main aim is to capture the Universal Championship

Given that Goldberg is not as agile as he once was, WWE may, despite Roman Reigns' absence, go ahead and have the former WCW icon lose his Universal Championship at WrestleMania 36, albeit to a different opponent. It is not yet known who will step up to the challenge and battle Goldberg at the Show of Shows, but there is a chance nonetheless that the replacement for Reigns could capture the Universal Championship.

WWE could simply book a return angle for Roman Reigns, where he would come back and chase the champion for the title - whomever that may be. The Big Dog has made it clear that he wants his championship back. He never lost the Universal title as two years ago of course, he instead had to relinquish it in order to fight a battle with Leukemia.

Given that the creative team would have planned some future feuds for the Universal Champion elect in Roman Reigns, they would want to bring him back to TV soon and seize the gold. This move would allow WWE to execute their original plans, giving fans an exciting title reign for the Big Dog.