There is a big chance that you fried at least the voltage convertor and maybe more IC's.
alt text http://i50.tinypic.com/2dkbqti.png
It's all tiny surface mount components inside, and replacing them can be very hard or even impossible.
I've done my share of smd-(re)soldering, both on existing hardware (wii-remote) and DIY electronics projects and it wasn't fun at all. One wii-remote got destroyed in the process, even though I used a $2000+ high-precision soldering station and knew what I was doing.
Besides, good luck finding the replacement components in singular quantities. Even Zoom themselves wouldn't start soldering smd stuff on their own devices, under warranty they simply replace the entire unit and the old one goes in the bin.
(there are similar posts like yours on the zoom forum and other places as well, all answers state that DIY-repair is out of the question)
Opening it up and saving the mic capsules is easy enough though, they are connected with little plastic snap-connectors.
Even if you're no electronic wizard, carefully opening pieces of gear can do no harm to anything other than the warranty (watch for screws hidden behind stickers/seals - they void the warranty). I opened up many pieces of equipment I use regularly just because I was curious what's inside.