I will add that is it theoretically possible for a sql guru to combine the databases into one because most tables have dual unique identifiers, ie the mp_Sites table has SiteID and SiteGuid. All the existing dbs probably have the same integer 1 for SiteID so they would clash if you tried to insert the rows with that, but since the SiteGuid is unique one could insert the row without SiteID and it would get a new SiteID on the row, but the relationships to other tables ie mp_Pages (one example) could be restored by queries based on the matching SiteGuid to update the SiteID in related tables.
but it would be a tedious process, probably error prone, and only possible to try by someone who is a real sql guru who understands all the tables and data. so probably not feasible for most people, but still theoretically possible for some