Leo was talking to vitality after trexx drop and is now trialing with them. You dont do that if you arent interested.
brother... you dont seem to know the market. Sayonara was so hot of an asset that most teams were willing to make room for him no matter what. Cojo himself admitted that they lost in the fight for him despite trying their best. Vitality just made a more compelling offer.
Leo is out of contract with FNC so the chance that Leo "replaces" Sayonara next year was nonexistent. They would either play together or only Sayonara because Leo chose another team. Even then... it would be more likely that they would drop chronicle (whose contract also runs out next year anyway) then miss out on Sayonara.