In an assault/battery with dangerous weapon domestic case, if the victim does not show up, will it be dismissed?

Possibly. It may also be continued for the witness to be located, particularly if the no show witness was under a lawful order to appear. If there is even a hint that the defendant is involved in the decision to not appear, additional charges might arise. In your example, whether the mother needs to appear or not is also dependent on what, if any, statements the defendant voluntarily made to police or others, and what evidence independent of the mother is available to the state.