Remove user from Response Groups in Skype for Business and Lync,

Remove-CsRgsUser.ps1

#Skype User Offboarding Response Group Cleanup. UcMadScientist.com

#Define user account
$SipAddress = "Button.Mash@EquestriAero.com"

#Create an array of response groups containing the user
$RGSGroups = (Get-CsRgsAgentGroup | where {$_.AgentsByuri -contains "Sip:$SipAddress"})

#Run through the groups and remove the user
ForEach ($Group in $RGSGroups)
{
  Write-output "User found in $($Group.Name). Removing..."
  Try 
  {
    [void]($Group.AgentsByUri.Remove("sip:$SipAddress"))
    Set-CsRgsAgentGroup -Instance $Group
    Write-output "User removed from $($Group.Name)."
  }
  Catch
  {
    Write-error "Error: Something went wrong removing the user from $($group.name)"
  }
  #Check if we left the response Group Empty
  if ($Group.AgentsByUri.Count -eq 0) {Write-Warning "$SipAddress was the last user in $($Group.name). This response group will not function until another user is added!"}
}