I found an informative blog post discussing the some common approaches to AWS DMS rollback. 

The blog post outlines a range of strategies, each needs to be considered and used in the relevant situation. The strategies range from basic to more complicated architectures - where a fair amount of skill & knowledge is required

A summary of the strategies

Basic fallback - 

Dual write

Fall forward  - Avoiding the loopback effect

Migrating a portion of a system or piecemeal migrations

Consolidating systems

Migrating an interdependent system of databases

Consolidating systems - Multiple systems into one system

Migrating an interdependent system of databases - 

Bidrectional replication 

Click  through to the full blog post Rolling back from a migration with AWS DMS