Well, the unions in Ryanair could obviously call for a strike to prevent the company from transfering their flights to their other airlines. That has already been done elsewhere in Europe.
The problem is that the unions in Ryanair don't seem to be working together. Some strike in august, some in September,...you get my point: easy for the company to cover the strikes by sending people from other bases to cover them.
Now if all the unions in ryanair, from every country, were calling for a single common strike to stop the development of Laudamotion/Buzz/Malta air at the expense of the Ryanair employees who have better conditions, then maybe things would change a little.