Where did anyone get the idea that Fedora was originally cast as Abner? I haven't heard that one before, either. Is this just your personal opinion?
I've always had the impression of Abner being very close and very protective towards Marion because he's his only child. I mean, his wife is dead or gone, so Marion and his work as an archeologist (especially the Ark of the Covenant, which was his constant obsession according to Marion) was all he had in life. I have a feeling he was very strict with Marion, almost a little on the possesive side.
I definately don't think he'd just abandon her. If anything, I personally feel that he simply didn't consider dying in Nepal and therefore did not think of providing some monetary way for Marion to get back to the US. This would explain her getting "stuck" in Nepal and possibly having to resort to prostitution at the Raven (at first), just so she could survive. My source for her possibly being a prostitute comes from the novelization of Raiders where she says she worked at the Raven and she says she "wasn't exactly the bartender..." I think the owner of the Raven knew she was desparate and the bastard took advantage of her. Poor Marion! Of course, the owner eventually went nuts and he gave Marion the bar. However, in the source book for a Raiders of the Lost Ark role playing game, it's suggested that Abner hid a small cache of really valuable artifacts in the floor of the Raven. He probably died before telling Marion about it.
Indy and Marion searched for Abner in the Further Adventures of Indiana Jones comics and the way it turned out was very interesting. Far fetched, but interesting.
If we see Abner in Indy IV, my guess is that it will probably be in the context of a flashback. I would like to see that myself. I sure hope this Indy/Marion mystery is solved in Indy IV. It's been bugging me for years.