Well, source code is one of the players. As this is the ultimate goal of the software project, it's clearly a winner, so let's pick the next runner up.
Source code history, versions repository ? Not unless you do some serious branching.
Backups ? Who needs them if there are originals ?
Architecture ? Documentation ? Can be recovered more or less easily as soon as the team is intact.
Test results, planning, meeting records ? Unlikely...
And so I argue that the next worst thing to lose would be the list of bugs and here is why:
- There are hundreds of unrelated items. There is no way anyone could keep any significant part of the list in one's head.
- There are no rules by which they can possibly be recovered.
- Each item was produced by more or less hard knock, sometimes even from an angry customer. Going through this again would be painful.
- Each defect is a ...uhm... defect, something that's not right with the project, something that should bug you until you fix it. And now you know that the thing just became a can of worms and there is no way to fix it.