[gizmogwai]

No, they don't. Behind the scene, it's Lucene that is creating a set of inverted indexes. While extremely performant for text search, it is also destructive and partial comparing to the initial dataset. So, there is no way to migrate an index to another one.

[lobster_johnson]

ES, by default, stores the original document in the nested "_source" document, which could be used to reindex data from scratch.