He shouldn't be a "guaranteed starter" and he's already making "star player" (for Everton) wages. Makes no sense to keep him, nobody re-ups for 50% off their current wages.
Plus, I didn't say both. I'd keep Gana another season. But if he demands 2+ seasons at his current wages? I'd let him walk, too.
People overrate the importance of "returning" players. If the new signings are on sensible wages (most) and signed for 4-5 years, then it's better financially even with the transfer fees.
When old/declining players are on high wages, you let them walk. Otherwise, you just throw more good money after bad, even if there's no "fee."
Next season, we'll be having this conversation about Tarks.