That sounds like a title of an Si Fi movie. 

I usually buy things with one reason.  If I want to chop wood, I will go buy an axe. If I will start using oil instead of wood then i will not need axe anymore and then I can sell it.  So. if the reason why you bought Yoda and Alisa changed. Or if Yoda and Alisa changed and dont fulfil your need anymore then you sell them. If they are same and your needs are same then of course continue to hold and use them.