HI, what I understood that you have a workflow and you assign some steps to some users but may be some of these users leave the office so you want to delete these users.
from my point of view, it will be better to assign the step to the group and give the group individual step assign privileges so the user can assign the job to himself and complete his work
1-it will be better to assign the step to the group and give the group individual step assign privileges so the user can assign the job to himself and complete his work.
2-you can make a step that assigns the job to the user inside the group this step will be an excutable step that calls windows or WPF application assigns the current job to the user inside the group if you use the web I can tell you how to make this using Launch URL or writing custom code.
3-bad way to open the workflow and change the assignment again from the deleted user to a new user.
regards,
Mohamed Massoud