Typically, when an Admin By Request tenant no longer has any paid licenses, it will fall back to become a Free Plan tenant. This means only 25 workstation licenses, along with 10 server licenses, will become available for use.

The implications of this are:

For the 25 available licenses on the devices where the ABR client is installed, both end users and portal administrators would be able to continue as normal; request an elevation, approve requests and so on.