I'm starting to think the show, or Don's story at least, will end with him getting out of advertising all together. Now I don't have much to support this speculation but way back in season 1 episode 9, we see Betty get a modeling job from McCann and Jim Hobart tries to poach Don.
In the end Don stays, and he tells Roger this and they have what might be a fairly significant exchange especially now that Don is working for McCann and doesn't seem to be too concerned with it.
Roger - 45 and no security, what's in it for me?
Don - If I leave this place one day, it will not be for more advertising.
Roger - What else is there?
Don - I don't know life being lived? I'd like to stop talking about it and get back to it.
Now considering Don doesn't seem to give a shit about his new job I wonder if this is exactly what's going to happen. Obviously you can argue that Don already went back on that when he left to form his own agency along with Roger and the others in season 3, but I think in that situation it was still his own company, where as now he doesn't have his own company he's now one of many creative directors, but that might just be semantics on my part I admit.
The one thing that gives me doubt besides this all being baseless speculation is that Don leaving advertising to live his life almost feels like it would be a happy or at least hopeful ending and although I'm not opposed to that the tone of all the episodes so far suggests we'll be leaving Don in a bad place by the time the series ends.
Then again season 6 had a bleak feeling too, one critic said it had a circling the drain feeling and yet that season had a somewhat hopeful ending with Don taking a step by finally showing his kids something about himself that was real. This is just speculation from me of course, so I won't be surprised or upset when everything I've speculated on here turns out completely wrong.