How to update requestor, when the current user is leaving the company

Need to understand all ways PO requester name can be updated to a new person when old person leaves. The new person will need to be able to submit change orders from the requisition side.

1.The requestor is leaving company, is there a way for him to assign to his replacement.

2.If person left and after that the supervisor knows who is replacement what is the process he can use to mass update the requestor.

3.If there is any approach which can be taken by IT from UI to update requestor. We need to look for in both the places PR and as well as PO.