RED, head office and backup office

Hello.

Let's say we have a Head Office  running an XG (physical appliance) with the needed licences.
20 RED from Remote Offices connect to this XG, everything works.

 

We want to setup a "in case of issue" Office (backup Office, call is like you want), also with an XG (virtual appliance).
The Remote Offices RED will be setup to use this backup-office-XG as failover gateway.

Do we need full licences on the XG of the backup-office to deal with the RED?
Or will the main licences (from Head Office) are enough?