Ensemble Studios has been defunct since 2009, following the release of Halo Wars. Age of Empires II HD was released under the Ensemble name, however this was more as a nod to the studios legacy than a venture in itself. If anything, you should be directing the petition towards Robot Entertainment seeing as the studio consists of former staff members from Ensemble.
http://www.robotentertainment.com/That said, I'm not entirely sure who owns the IP at present; chances are that Microsoft do since Robot didn't take any of their old IPs with them. Making it an open petition appealing to both parties might be more beneficial.