The final four: Drew McIntyre, Seth Rollins, Dean Ambrose, and Mustafa Ali

After Drew McIntyre goes on his rampage, he'll be faced with some familiar people. Seth Rollins had his battles with McIntyre throughout 2018, but dangerously, he'll be facing an even more personal enemy in Dean Ambrose, who will antagonize him to the end.
Mustafa Ali will be the wild card. He's been getting a big push ever since debuting on SmackDown in December, first having a lengthy match with Daniel Bryan, then pinning him, and then being the star of the fatal five way to determine his Royal Rumble challenger.
Look who just shut down all of Tony Khan's critics! More HERE.
Ali didn't win there, but that probably means that an even bigger push is coming for him, since it won't mature too early. To cement Ali's new push, he will make it to the end of the Royal Rumble match, only to find that Drew McIntyre is too much for him.
During the distraction in the aftermath of Ali's elimination, Seth Rollins will strike and finally eliminate Raw's "king of the jungle," leaving only him and his perpetual frenemy, Dean Ambrose.