Aidan-mun: As a player of a VtM character that probably makes Tristan pee himself a little, perhaps there is something Aidan could do. I'd have to talk to Cat-mun about this....but Aidan is not only an Infernalist he is also Baali. His magic and knowledge of demons and the occult is vast.
Perhaps, and I would be willing to accept that by him learning to do something like 'cure' a Malk, people might want him dead, but, maybe a ritual or some other creepy deep can be done to strip Adrien of his insanity.
Aidan could 'put' it in an empty 'vessel' or something?
However, there would have to be a good reason for Aidan to help him, as he is pretty much all about helping himself.
Something to consider....
Adrien-mun: This has serious possibilities.
Malkavians have sort of a hive-mind through the Madness Network. Some of them think the insanity and the Madness Network is Malkav still living within them, and when he wakes, he'll kill all his followers. Sabbat and Camarilla Malkavians alike believe the best way to avoid that is to dilute the blood as much as possible.
The Madness Network can be used to summon Malkavians from a long ways away. They go into a hive mindset, and many of them have no clue who summoned them or why they came. Some never remember what they did while they were there. The Madness Network is also used by Malkavians to divine the future and answers to important questions. I have read that any sane vampire that tries to learn how to access the Madness Network is driven insane. Perhaps putting the curse into a demon under Aidan's control might make it easier for Aidan to use safely, though.
Also, if Aidan is looking for old books or things, Adrien still owns a small 14th century castle on the outskirts of Moulins, France. It's been condemned for over a hundred years, but Aidan might find something useful inside, and the alarm that Adrien would get would give them a good reason to meet.
It occurs to me, that since Adrien never actually even mentioned the word "Malkavian" before killing the Malkavian Victoria, perhaps it would be easier, lore and magic-wise, if it was not that Adrien actually was Malkavian, but was instead suffering from lingering effects of the diablerie. *shrug* A thought. That would make it less like "curing" a Malkavian and more like "disinfecting" a usually-sane vampire.
Catherine-mun: Thanks for the comments, poke and email. All of the above seems possible and probable if there is a reason for Aidan to help. Anything I say from here in out is only opinion because I feel that whe I create a muse and give them away, it is up to the other mun to make them theirs and take the primary seat in deciding how that character gets played within the foundation that was set for him. Therefore, *in my opinion I'd think that the artifact/book/etc would have to be something of utter infernal worth. Because any archaic book, even of worth, wouldn't move Aidan to help especially since the price is high for Adrien finding out more about him than any outsider ought to know (in his eyes).
Chelle, if your taking him in the direction of being a Baali, than there are a number of infernal rituals open to him through his abilities that can strip Adrien or purify him. Aidan can basically write on if you see fit, although remember that comes at a cost (in the game it means spending blood points, here you can obviously write in anything). Luckily, Aidan is one of those pups that is old/strong enough to conduct/learn a new ritual w/o too much kickback (unless you want one...might make for an interesting thread).
Alternatively, why not think of using Adrien as Aidan's eyes and ears within his other contacts? I think Aidan would ask for a guarantee (usually it's a blood bond, but I am sure you gals can come up with something mutually satisfying).
If you can't find a way out, I'm going to throw out the potential of using Chandrika to strip the other "soul" from his body or something like that...buuuut I prefer reading about infernal evil and hard ass decision making ("If I do this, I owe HIM that...]
But to answer the question, yes, it is possible...Aidan is advanced in that he can damn well write the ritual himself that would be most useful. It doesn't even need to be an infernal one, actually. The Tremere's special brand of blood magic would do the trick. It would basically look like the ritual to break a bond. Aidan could alter it.