In the case of Ryback, he is not expected to be back to work for the company but it's easier to let his contract expire than to release him. His current deal expires later this summer.
The decision on Ryback's future was actually made before the May 1st Payback pay-per-view, where he lost to United States Champion Kalisto on the pre-show. As noted, Ryback was sent home from RAW the next day after a meeting with Vince McMahon over his contract.
A number of issues led to Ryback being sent home but they were said to be very far apart on money. Ryback wanted hotels paid for when traveling and wanted road expenses paid for. Ryback also wanted his contract to be guaranteed for the full term, that way if he was released for any reason, he'd still be paid in full for the length of the contract. While some WCW stars had similar deals years ago, that has never been an option in WWE.
On a related note, it was reported that Cameron was not on the internal list of releases but she got cut anyway. Cameron's tweet in support of Ryback's "equal pay" blog was seen as a major political mistake internally. She took the tweet down but the damage had been done.
Source: Wrestling Observer Newsletter
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