All calendar events disappeared Saturday at 10pm I checked the calendar and my events were there. When later, at 1am I checked again, all the events in the android calendar disappeared, while in the web calendar are still there.

How I can restore them?

I disabled autosync and did a manual sync, let some day to pass, did not resold the problem.
Open up main SETTINGS > APPLICATIONS > MANAGE APPLICATIONS

Press MENU > FILTER > ALL

Search for Calendar and Calendar Storage. Clear Data for both and then return to the Calendar App. Choose the Calendar(s) you want from the options within the calendar app (if you have more than the default calendar you wish to sync) and then sync.