Any Mashup which has a Parameter, also has a ParameterChanged event generated automatically.
The real interesting thing is what if you want to raise an event from the ContainedMashup to the Host Mashup.
In this case you can create inside the child Mashup an Expression with a DateTime output, with "new Date()" in the expression field and bind the result to a Session variable which is type DateTime. Anytime you want to trigger the event, just trigger the Evaluate service of the Expression
Then, on whatever mashup you want, you can use the Session variable changed event for event monitoring.
I have tried this similar concept of using session variable data changed, but in master mashup, when in the contained mashup there is a popup close happened, one of the service in the contained mashup changes the session variable value and this could be treated as a data change event for that session variable and based upon that we can use this event to proceed on anything but it is not working in my case. Have you tried anything similar?