The only remains of multiplayer can be found in the code:
00_54_00_0001:%s joined the Game! 00_54_00_0002:Reason : User close. 00_54_00_0003:Reason : Server full. 00_54_00_0004:Reason : Bad version. 00_54_00_0005:Reason : Bad password. 00_54_00_0006:Reason : Server lost. 00_54_00_0007:Reason : Server closed. 00_54_00_0008:Reason : High ping. 00_54_00_0009:Reason : Inactivity. 00_54_00_0010:You ran out of time. 00_54_00_0011:Reason : Wrong mission guid. 00_54_00_0012:%s left the game! %s 00_54_00_0013:!!! TEAM KILL !!! %s killed %s! 00_54_00_0014:%s killed %s! 00_54_00_0015:Enemy 00_54_00_0016:[ALL] 00_54_00_0017:[TEAM] 00_54_00_0018:[SYSTEM]
Question: Will there be any multiplayer features in the future?
2k answer:Mafia II is a story-based experience and we focused on the single player, story-based gameplay. However, we will have leaderboard support in upcoming DLC.
Source: 2k forum