as far as oxygen goes, a 10 buck battery operated pump will work as long as you need it to.
As far as heat, well, on my last set-up, I had thick styro-foam boards that skirted my stand (as before it had just been a very sturdy table). I always figured I could clad all 4 sides of my tank in the foam (as glass disapates heat very quickly) should I need to.
I now have only a nano, and personally would be tempted to use an old Omaha Steaks shipping cooler (have you seen those? They are like 3" thick with an airtight lid) as a holding tank for the live stock. That and a battery operated pump w/ airstone could keep things going longer than most emergency "plan B"'s, barring of course a $1000.00 generator.....