Those employees could have stood. Frontier and Spirit give vouchers out when they intentionally overbook.......which before the pandemic was everyday. If nobody takes the bait, they up the voucher value. For them it's essentially monopoly money.
If United couldn't get anybody to bite at the vouchers, then the employees should have stood the whole flight. Instead, they beat a man who was not fighting back physically. He only insisted that he get to his patient. They LITERALLY dragged him off the plane. By his ankle, as he tried to grab onto anything he could.