Question 1 : If they decide to delete my login, will it cause any issues with these Workspaces? Do they need to "Save As" a different file to prevent any issues?
Answer 1 : Yes. If they decide to delete your Login. All components like Work space, Segments, Bookmarks etc., created by you will vanish. They can use "Save As" but that is not the ideal solution.
Question 2 : Is there a way to transfer ownership to one of them? Or is this not necessary?
Answer 2 : Yes, there is a way and it is the ideal way to deal. In User Management, at top right, you can see 'Transfer'. If you use this option, you account items will be transferred to the respective Account you select. Go through : Transfer user account items
Also, number of Uusers can become a concern, but it will be increased to certain extent without Cost. Check with your Account Manager.