I´m looking into the possibilities of exporting a Unity prefab to the FBX file format so that it can be loaded up in Maya and/or Max. There´s a thread about it on the official Unity forums, but the first reply there contains a link to malware (Don´t click it!)…
Some time ago, before unity had a lightmapper there was a free lightmapper kit that included an FBX exporter named External Lightmapper Tool or something like that. Also, if you only need to open it in maya there is a pretty good maya exporter in the asset store. /eric