Stay - The inevitable feud with Roman Reigns once he returns

One of the biggest missed opportunities for both Ambrose and the WWE should he leave would be the inevitable feud with Roman Reigns once The Big Dog returns from his illness.
Ambrose didn't seem to turn on Reigns directly, and when asked about his friend by backstage interviewers, he seemed noncommittal, reserved and reluctant to answer any questions regarding the former Universal champion.
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But by 'betraying' Seth Rollins on the same night Reigns left due to Leukemia, he indirectly turned on his brother and the Shield.
Once Reigns is given the full bill of health to return, you'd have to figure that two things would be at the top of his list.
The first would obviously be to reclaim the Universal Championship he technically never lost. Like Finn Balor, he had to relinquish the title due to unforeseen circumstances. You better believe he's going to defeat whoever holds the title once his return is announced.
A second obvious thing on his to-do list would be to confront Ambrose about the turn and then likely feud with his former 'brother' over those actions.
Roman Reigns and Dean Ambrose have always fallen on the same side whenever they have been in the trenches. Only Seth Rollins has feuded with both of his brothers.
While Ambrose likely would have lost in that feud and perhaps that fact turned him off, the truth still remains that a future feud between Reigns and Ambrose would have been huge for the WWE and those two Superstars.