In SiteCatalyst admin, a custom event called Dropped Off was configured. Also a custom variable (eVars) was configured in which the name of last accessed field by user before she dropped off, was set.
As beforeunload event is triggered even when form is submitted, ensure that custom link tracking code is not executed. This can be achieved by making use of boolean flag which will be used to check form is submitted or not before sending data to SiteCatalyst.
You can find sample JS code at github.
In SiteCatalyst, report can be seen under Custom Conversion > Custom Conversion 1-10 > eVar Name
|Sample report in Site Catalyst|
Above implementation can be further extended to include form validation errors so as to track for which validation error user is abandoning the page.