1) You should have them backed up. Apple make it very, very clear that it's your responsibility to back them up: there is even a window that pops up in iTunes the fire time you download an item to tell you this. It's not Apple's job to protect your data (which this now is) from system failures, thefts or reformats
2) If you contact iTunes support and ask very nicely they might let your redownload: they have been know to in the past
3) Start taking regular backups: your harddrive could fail tomorrow