From T&B
If a master dies & a familiar survives, part of the master lives on in the familiar. It loses any extra HP's & skills it gained from the master but retains most of it's familiar abilities. it is treated as having a master 2 lvls lower (but never below 1st lvl). if the master is later brought back from the dead, the bond is re-established, and the familiar gains whatever abilities go along with the masters new lvl.