Availability Groups and Transactional Replication
Distribution database should not reside on the servers that are part of AlwaysON availability group that the publishing database is (or will become) a member of.


  Replication configuration is coupled to the SQL Server instance where the Distributor is configured; therefore the distribution database cannot be mirrored or replicated. 


If you want to provide HA for distribution database, then you have to go for SQL Server Failover cluster. Thats the only option.

Your scenario is as below :



So if you loose server C, the only option to get distribution running on server D is to do a RESTORE.. with KEEP_REPLICATION from a good backup. You can use this script to restore your distribution database (with some changes as per your environment). I would go for a clean install of replication !

Make sure you script out your replication topology whenever your do any changes. You should have handy scripts of both drop and create, so in a disaster situation, you have scripts that will help easily create replication.

Also, since you are using always-ON with T-Rep, I would suggest you to enable TF 1448.


  Trace flag 1448 enables the replication log reader to move forward even if the asynchronous secondary replicas have not acknowledged the reception of a change. Even with this trace flag enabled,, the log reader always waits for the synchronous secondary replicas. The log reader will not go beyond the min ack of the synchronous secondary replicas. This trace flag applies to the instance of SQL Server, not just to an availability group, an availability database, or a log reader instance. This trace flag takes effect immediately without a restart. It can be activated ahead of time or when an asynchronous secondary replica fails.


Reference : Configure Replication for AlwaysOn Availability Groups