#4 Dolph Ziggler
Dolph Ziggler has been under contract with WWE for 13 years now. However, for the last three or four of those, he has really been treading water. His gimmick on SmackDown Live right now is likely the actual manifestation of his real gripe with his current placement on the card.
Sooner or later Dolph is going to snap and realize that there really is nothing left for him in WWE. When the fans had his back not being pushed by WWE was probably bearable. Without their support what is there for him to stay for?
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He could follow in the footsteps of Cody Rhodes and Jack Swagger, but that really seems unlikely at this point. Dolph likes attention and he'll rarely get that from more than a few hundred people at a time on the independent circuit. He might give it a go but soon after he'll realize that if it isn't WWE, it's not worth his time.