Perhaps, but once again everyone has left because they either had another goal or had another obligation to uphold. Serena has neither, so even if she has to leave, I don't expect it for a while. And I don't think she would leave Ash just because "needs some time to complete his journey before he's ready for a relationship." She can easily keep traveling with him until that point. Gives her the chance to both find something for herself while also getting close to Ash. Unless they pull a "I must travel alone to find myself" thing for Serena.She'll have to go eventually in my opinion; it's like the law of the anime sadly. I personally hope that she gets some closure beforehand though. I'd be okay with her still liking Ash, but maybe she'd realize that he needs some time to complete his journey before he's ready for a relationship.