What can be done about the calendar app closing itself on an iPad?

This is how applications crash on iOS - so you may want to check your settings to see if your iPad is sending crash reports to Apple.

Settings App -> General -> Diagnostics & Usage

You can also look in the Data submenu from the above screen and scroll down to look for LatestCrash.plist and see if the date matches when your iCal quit.

In general, it's not possible (even as a developer) to read these reports without access to the iCal source code and you have some short term things you can do to isolate the issue further.

First is to remove any notifications (turn of WiFi and cellular data) and reboot the iPad. If iCal crashes, then it's due to the calendar data on the device and not some external cause. You can then remove your calendar information, account by account to clear up which account has the data corruption that is causing iCal to have a problem. Worst case, you will have to connect your iPad to a computer (iTunes) and force a sync to erase the calendar data on the iPad and replace it with data from the computer to clear the data that is causing the crash.

Apple will likely fix the crash (even with bad data - the program should handle it and let you know an event is broken or ignored and why) in the upcoming updates - but you can report the crash to add weight to this particular bug getting fixed.

You can also take an overkill (but faster) approach to erase all content and settings on the iPad and set it up again.

It's unlikely the data will come back corrupt from your calendar sources (or the backup) but if it does, at least you'll know a bit more about how to isolate which calendar is causing iCal to have problems.

Sounds like the April 1st calendar crash. Delete whole day events on April 1st (and unsubscribe from calendars that give you public holidays on that day), and that should fix crashes that occur when you go to month view in March.