This makes no sense physically unless Mira is moving through a thick dust cloud which is slowing down the ejecta. Otherwise there is no way the ejected material wouldn't continue moving through space at the same velocity as the original star (plus a radial component, so Mira would have a spherical nebula around it instead of a "tail").
The only reason comets show a "tail" is that there is a solar wind pushing stuff off of them in a particular direction, there is no analogy in this case.