Do you understand how hunt groups are configured? It goes a long way to pointing out the proper database tables.

You have the extensions in the table numplan, and huntgroups are based on line groups (you have a table linegroup), and they are linked with a linegroupnumplanmap.

Then there's an experiment you need to make: do you have a 0 length call record for each extension that has run in the huntgroup before the call was finally discarded, or do you have but one entry for the last line that has run before the call was abandoned? And unless you are using separate lines for the huntgroup and not the primary line, you won't be able to differentiate between a lost call that ran on one phone only, and a lost call that rang on multiple phones.

The kind of statistics you are looking for are common in a call center scenario.. if you go ipcc express, you'll get that info for free (after the price for the software and server of course).