The employee documented everything, but said documentation was not backed up by the company. Furthermore, the company did not train or hire an adequate replace

The employee documented everything, but said documentation was not backed up by the company. Furthermore, the company did not train or hire an adequate replacement for said employee for _six months_. This is a gross failure of leadership at the company, and the former employee has every right to negotiate compensation for the inconvenience of having to work for them again.