I think that if you want to make a valid argument, you have to stay in the realm of the mind. CrCo can be used to cure a blind or a crippled, thus removing the flaw. If a magus takes the flaw, it must be incurable in some way, otherwise the flaw does not make sense. But that is a balance thing, not a magic limitation.
This is the flaw:
If the Jinn agrees to kill somebody in the other part´s behalf, he is bound to try. That does not mean that he cannot be “magically restrained”, mind controlled, killed, paralyzed, stoped by a ward or another defect that the Jinn has, etc. A lot of things can stop it from fulfilling his part. If you drive that jinn insane (PeMe), is he still bound by the agreed terms? How so?
What makes “forget the agreed terms’ a different hazard?
I mean, I can imagine how can that creature be magical bound by the terms of the agreement like salutor says, when is something passive (if agreed not to do something, you cannot do it) but I cannot imagine how somebody that has forgotten the agreed terms could pursue something actively.
The only possibIlity that I can think of is that the Jinn can still feel that there is a bargain in effect, even if he cannot remember the terms. He can try to reach the the person he bargained with (but can he remember he/she?), perhaps. But what I mean is that time the terms of the deal may expire. Perhaps the thing that the Jinn has to do can not be longer done.
And that is perfectly fine. As fine as being magically paralyzed for the time in which that Jinn should have fulfilled his bargain.