Well… one could probably at least export the contents of teh calendars from the old database. There are four tables which are holding the calendars:
oc_calendars, which denotes all the calendars in the db. From there you will get the IDs, which you need to export the calendar entries from oc_calendarobjects, where there are the actual vevent objects.
In oc_calendarobjects, column ID and column calendardata should give you, what you want. Fire up some MySQL (or whatever DB you used to host the NC database) and use sql to extract your calendars into a txt file. Use that one to re-import your calendars back into your running NC instance.
You could use my script calcardbackup after firing up the old database to pull the two calendars from the old database and reimport them to the new installation. No need to fiddle around in the database then.
Have a look in the README of the repository for the section “does this work with a broken instance”.