if your wandering will model animations change, answer is yes.
Each model has its own animations, that can be changed in special tools (and with promition of author of custom model).
So changing a model will change its animation. So you cant replace (for example) a footmen with succubus and still keep footmen animations.
Is this what you asked. Your question is really badly put together.
From tread title name, you ask what model should replace this one. Well, you can use model that uses same animations, unless animations are custom made by creator of the custom model. That will make spell animations stay same and wont mess up (like when you order a unit to roars, and it bashes with his shield).
So, if that model uses beastmasters animations, then yes, beastmaster would be great to replace him.