Hi Alex, While the admin is still part of the company, he/she can assign any other admin. Once he/she leaves the company, nothing will change.
@Alex Steedman RC Teams administration is an absolutely nightmare due to limited/immature administrative features in RC Teams. I'd highly recommend you have clear and enforceable policies to govern RC Teams.
If I create a Team and mark it private, you - as an administration - can do nothing to take over the administration. I have to cooperate in order for you to join the Team and take control. If I leave, you would have to convince a Team member to copy/paste data from the Team and store it in a Word file or such for archival purposes and then ask members to join a different group controlled by you. Members may choose not to leave that group.
In our organization, we have a policy and manual audit to ensure that RC Teams are created by authorized individuals only.
@Mary-Community_Moderator RingCentral must definitely rethink their product design.