Once I've been involved in an outage where our mirrored servers lost connectivity. One of the things to worry about is making sure your applications are pointed to a single instance. In a network outage you can have all the nodes of an Always On cluster up but unable to communicate with each other. You force a fail over to a secondary and then as long as there is an outage you can have two primary nodes since the original primary won't know about the forced fail over.
Depending on the locations of your application servers, their configuration and their ability to reach a SQL server, then in theory you can have two nodes believing they are primary and having data changed at the same time. Once you fix your network issues and the nodes resume connectivity all the data changed on the original primary will be overwritten from the node where the fail-over was forced to. This can result in the loss of critical data.
I've seen this situation once with SQL 2005 and mirroring. And we decided to not to force the fail over and let it stay unreachable. Reason being that in the worst case if we had to back up and restore to restart mirroring, then it would be a 2 day process for us with risks of the transaction log becoming full and not being able to expand the disk on which it sat.