#2 Help Roman retain the title
If Dean isn't involved in a match, he could choose to assist Roman defeat Brock and Strowman. This match might be the hardest of Roman's career so far because both of his opponents have a score to settle with him, and they are also much stronger.
He also has a massive target on his back because he is the current Universal Champion. Taking these factors into account, Dean might decide to run interference in the match and protect Roman's title.
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Even if Dean interfered, triple threat matches are no disqualification, and Roman would still have the opportunity to get the win. This strategy has the potential to be successful because Brock is a lone wolf, and doesn't have anyone watching his back, while Braun took out his fellow Dogs of War mates, meaning he is all alone once again.
Since the WWE haven't officially announced the rules for the WWE World Cup match, Dean wouldn't be in a good position to help Seth Rollins win it like he helped him qualify.
Another reason why Dean wouldn't interfere in the fight would be because the numbers game would be against The Shield if the other competitors choose to gang up on them.