It should be possible to get the data back from your iPad, however I am not the iPad expert. Repost in the iPad forum and ask the posters there. Until then I would not attach the iPad by cable or wi-fi to do a local sync with iTunes.
No sarcasm intended here, try to be aware of your sync paths (makes finding conflicts easier) and a having backup is the only way to ensure that you will not lose your stuff, things break, get lost, get stolen, all hard drives will fail, the only question is who owns the computer when they do.
I hope this can be fixed for you.
Just don't open iTunes while the device is plugged in, and you can do an instant backup of what is left in Calendar and Contacts by opening the apps and going to File>Export, choose vCard format for Contacts (select all cards) and Calendar archive for Calendar