Why is their a deadline?
One of the purposes of a server merge with the guidelines of "only the active accounts within the last year is to be merged" is to clean up old, inactive data. Cleaning up databases makes them able to run more efficiently.
In this case, I'm not sure what exactly will happen with the data but there is that hard deadline. I suspect it will be archived and the retrieval after such will be extremely complicated. I'm not in charge of this however, this is only speculation on my part.