Today's N+1 is all about whether or not your ViewModel is Visible - and about how to kill it when it gets removed from the screen.
This is a fairly FAQ topic - see questions like http://stackoverflow.com/questions/15961664/viewmodel-lifecycle-when-does-it-get-disposed and http://stackoverflow.com/questions/19816819/how-are-views-and-viewmodels-freed-up-in-mvvmcross
MvvmCross doesn't provide any built-in event notification - but it is easy to add it for your app.
In this video, I show how to add and invoke interfaces like these to some view models which are shown by a standard MvvmCross presenter:
If you have custom presentation, then you'll need to adapt this technique to suit your needs - but, since it is your custom presentation, then you should hopefully be in the best place to do this.
The source for today's video is in https://github.com/MvvmCross/NPlus1DaysOfMvvmCross/tree/master/N-42-Lifecycles
The video itself is:
The audio skips in the first few seconds - making me sound even odder than normal ;)
For a full N+1 index, please see Aboo's fabulous work on http://mvvmcross.wordpress.com