Today you can get the ownership of the user's ODFB but if you delete the user, after 30 days, the user's ODFB is going to be deleted too...there is not current a feature to not only change the ownership of the user's ODFB but also stop the deletion process
You can see microsoft's article about deletetation at my first post, in initial setup
-OrphanedPersonalSitesRetentionPeriod i set it to 365. you can set it 1 to 3650 = 10 Year.
but i read this:
If the Manager field is populated for the deleted account, the manager will receive an email message that states that the site will be removed after the retention period expires, and that access to the site is granted to the manager.
in this case Manager will grand access after a year right?
I TEST IT
When the user deleted from AD, it mails to manager directly so it will delete after 365 days.