Most of them go back to 8/2002! I've been meaning to take time and read some of them for fun.
Hopefully they'll show back up and it was just a glitch.
I found this from 1/2011 They (messages SparkTeams) will stay on there forever. If it is a message board though, if it hasn't been posted on in a while (I believe around 6 months), the message board is archived, but still on the site.