DAG two member

I have a DAG with two member (MBX1 and MBX2) and two CASHUB servers (CASHUB1 and CASHUB2) . I have configured the witness in CASHUB1. All exchange servers are in the same AD site.

All Exchange servers are virtuals and I have this distribution.

HOST 1 (physical)        HOST 2 (physical) 

MBX1                           MBX2

CASHUB1                    CASHUB2

if the Host1 go down (or Turn off) the failover is not automatically because witness is  unavailable, what Can I do to restore the service on host 2?.  By another hand,  I have configured alternative witness in cashub2.

I this scenario I have to run Restore-DatabaseAvailabilityGroup? consideringthat all serversbelongto the same AD site.