For those of you have wondered what happens when a Cloud gets untrusted? Let me answer that for you. If you have a domain that is trusted to the other Cloud and for some reason someone decides to untrust that Cloud. The Cloud that is trusted domain access gets revoked. But what is worse is that users that are associated with that domain are removed. So it is very important that you do not untrust a domain from another Cloud unless both parties have agreed on this. Because this will cause some serious downtime to repair the damage on that Cloud.
I would recommend that if you are trustee to a domain configuration its a good idea at least once a week to download a copy of your users list and put that file in a safe place. This way if you have this happen then you have a backup of the users to quickly put them back with minimum downtime.