Couldn't find this in the documentation, so I'm noting it here in case it's helpful to anyone else.
I wanted to determine the sort order for a table before the user left the page. The subsequent page presents the table's contents in a different way, but I wanted to do so using the same ordering that the user had set using tablesorter.
How to achieve this? After quite a bit of head scratching, I found that tablesorter adds a 'config' property to the table, and you can access the sorting details at table.config.sortList.
sortList is an array with the same format as the sortList configuration property described in the documentation: the elements '0', '1', etc. represent sorted columns ('0' is the primary column, '1' the secondary, etc.) Each of these contains two subelements: '0' is the column number (zero-rooted), and '1' is the sort order ('0' = ascending, '1' = descending).
So for example [ [3, 0], [0, 1 ] ] tells us that the table is sorted primarily by the fourth column, ascending, and secondarily by the first column, descending.
Note that the table object is passed as a parameter to the sortEnd() function, so one option is to update your records every time that is called.