In Conga Composer Release 8 there is no longer a Conga Mail Merge tab. This means if you are upgrading to Conga Composer Release 8 your Conga Mail Merge tab will disappear. Individual Conga Mail Merge solutions created prior to Conga Composer Release 8 will NOT be changed or removed; you simply need to separately install the new Conga Mail Merge add-on.
Conga Mail Merge will need to be installed as a separate add-on (free of charge) to continue running Conga Mail Merge solutions. To do so, see Installation Links for Conga Products.