After Oh Shit!, Attis has been hurt but he certainly is not dead yet. A small intermezzo with Attis' mouth follows in lab Three, and the Initiate meets with Patty, who is caught by the blob. She gives the keycard to open the door to the final section of Lab Four. The vault's selfdestruct sequence needs to be started here, but naturally, the blob is blocking it. Go for another round with him, using the best weapons you've got. The fight will be a bit easier, as Attis is weakened and has lost his suction powers.
Finally, the blob retreats from the console and the selfdestruct sequence can be initiated.