The master.vmp file is the master version map that contains the GUIDS for all of the objects and the version of each object that currently exists on the server.
When the server starts, it looks at the master.vmp file and attempts to find each of the objects referenced in the file. If there are objects in the data directory that don't have a corresponding GUID in master.vmp, those objects are deleted. If the master.vmp doesn't exist when the server starts, the server creates a new master.vmp file and deletes all of the objects in the data directory.
If you lost the master.vmp file, then everything in the data directory will be deleted from the data directory, and there is no way to recover the database unless you either have a current backup of the database OR have a copy of the database project as it existed on the server.
Support Engineer, Microsoft SQL Server