If you have access to the server console, you could manually add them back in with ulx groupallow. If not, you could edit the "superadmin" section in your data/ulib/groups.txt to the default.
"superadmin"
{
"allow"
{
}
"inherit_from" "admin"
}
but, anything specifically added to them otherwise will need to be re-added ingame.
It's easier to use groupallow, though.