Anybody else finish melissa's mission before meeting papa? She dissapears, and even if I talk to regis about him taking over, and then try to slip a grenade in his pocket while sleeping (while stealthboyed) regis will then give me no further dialog and I fail both Oh papa and Can't we be friends. I heard Sandman might work, and somebody else suggested I wake him, and then lead him out to the desert to kill him. It just svcks that they didn't figure this out in playtesting. I can finish every requirement to complete Oh Papa, except melissa, because I like to explore. Bummer.
Yes, it happened to me too. Oh Papa is off the table unless you are on PC but you can still finish the quest for the NCR. I talked to the NCR commander at the dam and she told me to assassinate Papa. Only then would Regis talk to me with positive outcome.