VBS validation warning for multiple assignments in Resign

Summary:

Set up a custom VBS warning when someone is resigning and has more than one assignment

Content (please ensure you mask any confidential information):

We'd like to be able to set up a custom VBS warning when someone is resigning and has more than one assignment
We've switched off the function to select Assignment as we want don't want employees to be able to end an assignment, only HR and Line managers retain that. But we would like to be able to remind people that if they are resigning they will be doing so from all assignments. So if possible we'd like a warning that pops up if someone with more than one assignment is using the Resign from Employment action.