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I don't think cross-region replication would've helped in this case:

"The replica tables are intended to serve as read-only copies of the data; however, it is possible to write data to a replica table. If you write data to a replica, those changes will not be propagated to the master, or to any other replicas."

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You can relatively trivially build multi-master cross-region replication in DynamoDB by using kinesis and writing to kinesis instead of DynamoDB directly. On the consuming end of Kinesis you then fan out to all the DynamoDB (or whatever other database you want to use) regions[1]. Admittedly this only works with some relatively relaxed constraints on the latency you can see, intra region latency can go up to 1 second although rarely, while cross-region is around 3 seconds. An important role is also played by the structure of your objects and how accepting they are of concurrent updates coming from different regions (which is the main reason why the default replication in DynamoDB is not multi-master).

[1]: http://tech.adroll.com/blog/data/2015/06/26/kinesis.html

You could at least fall back to a read-only mode. That could be very helpful, compared to going down completely.

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