At this this time Skype for Business has not been officially tested. If the Lync client itself is updated to Skype for Business MessageStats will still gather and report information from you Lync environment since MessageStats gathers from the LCSCDR and if available the LCSLOG databases associated with Lync.
If the Lync Server is upgraded to Skype for Business 2015 this has not been tested and is not currently support for use with MessageStats or MessageStats for Lync.
STATUS
Currently, there are no plans to support Skype for Business in MessageStats.
Unified Communications Command Suite-Analytics is planning to support Skype for Business in either version 8.1, or later.
https://www.quest.com/products/unified-communications-command-suite-analytics/