I do get the impression that David is pictured as the "victim" in here, maybe I'm wrong.
What we do know is from David side, because he is the one often questioned about Mark and of course a co-founder of Dire Straits, but we never listen from Mark about it. Even if questioned, I doubt he will give an answer to please the tabloids curiosity.
Remember it is Mark we are talking about, a very tough and strong personality. As any of us must have experienced in their own life, it is very hard to work and live close to such personalities, you either accept their greatness and find a way around to make your ideas forward (John Illsley), or you part ways and say you would like to explore your own ideas instead of working for those of some one else. The parting away might not be as graceful though, leaving scars which even time can not heal. Mark even had a fall out with Dylan after "Infidels", his own idol, that shows how strong he is and how much he believes in his own way. That does not mean he is always right, but one must have a really hard time to convince him otherwise.
In his whole career Mark has taken solid decisions, producing his own albums as soon as it was possible for him, exploring new ways and arrangements album after album not afraid of public reaction, leaving Dire Straits at sabbatical at their peak to work on more down to earth projects, leaving them for good to pursue his own style splitting in the way with Ed Bicknell, a great manager.
If the two brothers get together, it will be a great story, but if they can make great music together, that should be the aim, I am here for the love of Mark's music after all.