You can use try/catch in Powershell. It looks like:
Get-Content "C:\Users\blabla\users.txt" | foreach {
Try {
Remove-QADGroupMember -Identity "usergroup" -Member $_
}
Catch [System.Exception] {
"$_ isn't exit"
}
}
I didn't run the code. You can do some tuning on it.
http://blogs.technet.com/b/heyscriptingguy/archive/2010/03/11/hey-scripting-guy-march-11-2010.aspx is a good post on this topic.