If Rey Mysterio goes to WWE, he could still wrestle elsewhere.
According to Wrestling Observer, Rey Mysterio has still been in talks about joining WWE. Reportedly, Mysterio wants a deal similar to Chris Jericho's which is part time and allows for Jericho to play music, be on television, and do his cruise. Jericho originally was not wrestling anywhere else besides WWE but then faced Kenny Omega at Wrestle Kingdom 12. Jericho then appeared at Raw's 25th Anniversary and will be wrestling for New Japan Pro Wrestling again in March.
Mysterio recently appeared at WWE Royal Rumble as the 27th entrant in the men's Royal Rumble match. He lasted nearly ten minutes in the match and his physique was visibly changed. After his appearance, there were reports of him possibly signing with WWE but they have not happened yet.
Mysterio has now been scheduled to face Jushin "Thunder" Liger at the same New Japan Pro Wrestling event in March at which Jericho is scheduled. Also today, reports surfaced of Mysterio's son starting to train in professional wrestling.
Fightful Wrestling will update any reports or confirmation of Mysterio's future.