user – SharePoint Online and Flows – how to remove quitted employee correctly?

I created flow that uses “Grant permissions” action, and it uses SharePoint Group with users. One of employees has left the company, and (as I understand) IT Team deleted this account. But this user was still in SharePoint Group so my flow got his email and crashed on “Grant permissions” step:

cannot resolve user

So all my approval instances created yesterday crashed.
As I suppose IT Team should not delete user, but reset password and disable(?). Imho we need to keep users for audit/project management history..

What is correct procedure of removing resigned user in Microsoft 365? Do You have any best-practices or what do You use?