I believe that it will be possible to rebuild our packs even without Mitsu support, one reason I picked the car was the use of only 88 large format cells that are bolted together, something I'm confident I could rebuild myself.
Owners of the original Honda Insight have a couple of pack rebuilding options available. I could see a couple of list members forming the core of such an effort by providing the battery trays from salvaged cars to serve as 'rebuildable cores'.
Here are examples of EV pack building/rebuilding entrepreneurs, some providing rebuilds, others just a how-to guide. I have personal experience with and could recommend the first few.
http://www.hightechsystemsllc.com/pt_Batterypacks.html
Derek is the leading builder of racing packs, but it would take some work to ensure compatibility with our cars' BMS
http://www.manzanitamicro.com/
Rich and Co. have done several 'orphan pack' rebuilds.
http://www.autobeyours.com/MASP%20autobeyours%20as%20a%20tenant.htm
Steve is an incredibly entrepreneurial Prius rebuilder, he finished off an incomplete Azure Dynamics/ Ford Transit Connect Electric as his shop truck.
Here's a quick weeding of google results, some may be vaporware.
http://www.batterymd.com/electricservices.html
http://www.evcenters.net/services.html
http://www.priusrebuilders.com/
http://www.hybridbatteryrebuild.com/
http://www.hybridrevolt.com/catalog/
http://www.hybridbatteryrepair.net/ (these guys abandoned the Insight market)
http://greentecauto.com/about-us
http://hs.thehybridshop.com/conditioning-quote
