I think you will be fine as long as you keep the media wet. I've had power outages of a couple days and did not experience any issues with respect to the biological filtration on tanks with similar set ups (ie sponges that were running in addition to canisters/HOBs).
With a canister filter, I would empty the water out of it and unplug it if the power outage is going to be more than a couple of hours. As long as its wet, it'll be fine, but if it runs out of oxygen, you're in trouble. With no circulation, you can get serious decomposition, and low oxygen. With it emptied, you'll have basically infinite oxygen -- so you just have to restart it when the power is on.
As an aside, filters are one of the things you should generally unplug during a power outage anyhow. You'll often get power cycles where it comes on, goes off, comes on, goes off, etc. This can cause problems with a lot of pumps, including filters, where they won't start back up. Plus, having to plug them back in and restart them guarantees you have restarted them -- I can't tell you how often I've found a pump not running after a power outage.