The characters have three choices for leaving Velkynvelve: the north, west, and south passages.
Menzoberranzan and, eventually, Blingdenstone (see chapter 6). Most of the characters’ fellow prisoners discourage travel toward the drow city… 26 days plus 8 to Blingdenstone
This leads most directly toward the Darklake 8 days
This leads toward the duergar city of Gracklstugh, following a south-westerly route. 28 days
If I recall correctly I think the consensus was the Darklake but correct me if I’m wrong.