Yes! You need to have Comic Life for iPad 1.2+ installed, and Comic Life 2 for Mac or Windows. Instuctions here on how to get your comic from your iOS Device onto your desktop.
Firstly, create a comic on your iOS Device - just to setup the Dropbox folders - then Export > Copy To > Dropbox.
It will export it into your Dropbox account in the /Apps/Comic Life/ directory.
Once synced, to your computer, then you can open this file up on your computer. Make changes, and save back into the same spot.
Then on the iOS Device - click the + button to create a new comic, and then Copy From: Dropbox - and import your comic again from Dropbox.
Once you have done that once, you can then create comics on your computer, and save them (choose "Comic Life 2 Archive" from the drop down File Format menu) to the Dropbox folder where Comic Life 2 for iOS Device looks (in your Dropbox account in the /Apps/Comic Life/ directory).