When the mage dies, like other creatures, he is immediately destroyed and removed from play along with anything attached to him. There are a few additional restrictions that don't normally apply to other creatures, such as being unable to pay any mana for things, but for the most part it follows the normal creature death rules. I'm not really sure the problem here.
I believe Kharhaz would like the game to end immediately upon Mage Death, which is a reasonable argument, but it currently doesn't end until the phase finishes. Basically, the game can't end mid-phase which does allow time for the other Mage to be killed. Basically, if both deaths happen in the same phase it is considered simultaneous.
I'm not sure the issue with Magebane, because the Mage takes the Magebane damage after resolving the attack. As in, the Mage doesn't get to complete an attack after death and isn't working different from other creatures. The comparison to a damage barrier seems apt.
That said, I think the rules could definitely be simplified, but I don't think that's the games biggest problem and the changes I would like to see actually aren't possible without rewriting the game to a significant extent. Maybe a new edition will see them. Stuff like simplifying traits and conditions, cleaning up the spell restrictions and training rules, and yes the order of operations could use some attention. I agree with all of that, but those are significant overhauls to the game. Basically, after nearly 6 years, I feel we've learned a lot about how this very unique first of it's kind game operates and we can do better. But not without making a whole new game.
But again, that's not really the problem with the game. The real problem is output and support. LCG's tend to get an expansion per month. We've gotten 1 or 2 per year. To put out more expansions they would need to prepare more material in advance, because there's only so much you can do to speed up playtesting. So, there's no way for us to really fix that with the game already being out there, it's something that would need to be planned for pre-launch. They then also need to fix their support for the game, maybe approaching it more like a miniature war game than a CCG, but I don't really know. That's an area that they really haven't figured out yet imo, with even the GenCon tournament still experimenting on how to run things (no more timed victories this year).