DR Site availability if primary goes down
Technically, yes, you should still be able to read from the DR instance assuming it is configured as a Read Only replica and you are connecting to it directly (As read only routing through the primary would not be working).

You should really be concerned in this case though about bringing the DR site online as the new primary replica.  You would need to force quorum on the DR site, and manually failover (with possible data loss) so you can then accept reads and writes at the DR site.

Perform a Forced Manual Failover of an Availability Group (SQL Server)