If a slide is removed from Master deck in Slidebank, it will simply disappear from any Virtual presentations that it has been used in.
If an older version of the Master deck is restored (to include the removed slide), the slide will once again populate Virtual presentations that had previously contained it.
The Virtual presentations will always reflect whatever is going on with the original versions of those slides.
Please note that only the slides you have actively chosen for your Virtual presentation will be affected.
For example, if a new slide is added to a Master deck, this will not be added to any Virtual presentations (until it is actively chosen when building/editing a Virtual presentation).