1. Friend Online notification
The friend online notification would be more useful if we could flag which friends we want to be notified for.
Alternatively, put the friend's name in the notification.

2. Offline messaging
Instead of a message saying "character not found", how about "message pended till character online".
You could expire messages after 24 hours

3. Party play
So I want to play the Dead City with my buddy, however we don't want to be destroyed by the boss.
How about allowing others to join the game in the two remaining slots, the same way they would be able to if we weren't partied?
Perhaps an Exclusive/Joinable option on the party page?