In one of our clients, we had the same requirement that, once the Accounts Directorate approved the workflow, then workflow should trigger to 2 different Executive Directorates depending on whoever is available by that time. Which means, any one of the 2 EDs can take approval action if they are available and then workflow will be completed.
Finally we agreed with the following.
-- Once the Accounts Directorate approved his part, work item will be triggered back to him again in the next level of approval. Then Accounts Directorate will check internally who is available (holding the Executive Directorate position) that time. And based on that, he will re-assign the work item to the next available Executive Directorate.
Sounds cheesy but this is how we convinced the client
You can do the following.
1) First decide if above solution is acceptable in your case.
2) Once the client accept this, you need to set the appropriate roles and privileges for those managers so that they can take an action in the workflow once this is triggered to them.
3) Also you have to check the privileges for that person too who will be doing the re-assignment activity in the workflow.
4) Additionally, we had set email notification where the subject line of the mail will be picked from the workflow subject. Example; if the work item is for Executive Directorate approval, then you have to mention this in the workflow subject. So when the mail triggered for approval again to the same person (in our case, this is Accounts Directorate), by looking at the email subject, approver can understand who has to take action this time in the workflow and based on that, he/she can re-assign this to the correct person at the next level. This step will erase all confusion for the approvers.
Regards,
Sourav