Merkel would never enter a coalition with the Petry-AfD.
Even if FDP were unavailable and the only other option were yet another grand coalition with the SDP?
Since Merkel is completely devoid of any ideology but stalwart extrem centrism, she has no problem at all with opting for the SDP as coalition partner, same as she would not with the FDP and probably also the Greens. She does have problems with any sort of "radicalism", to put it that way, anything a bit further to the right or the left of the aforementioned parties; so coalitions with AfD or any other rightist party that may arise in the future are an absolute no-go for the Merkel CDU.
There's also still the old "catchphrase" of former Bavarian MP Franz Josef-Strauß - "no established party to the right of the CSU" - so CDU/CSU will go to great lengths to ensure nothing to the right of them gets "established". A coalition with the AfD would just be "establishing" them, so there is another reason to oppose that.
I liked that the politico article mentioned both Kohl and Bismark, not sure if Merkel will rank as high as them. Is she likely to win?
She is dead set to win. The question is more by how much she will win, that she will win is out of question.
Well I suppose hypothetically (assuming the FDP fail to get back in) there could be a broad red-red-green coalition, if the lefties are collectively sick of being the junior whipping boys.
Polls in Germany have been so boring lately.
I don't think any coalition with the Linke on the federal level is likely in the near future. The Linke still has the old SED/DDR/Stasi-feeling attached far too much for it ever (at least in nearer future) to be "mainstream" enough to be accepted into a federal German governing coalition. If the SPD entered an official coalition with the Linke, it would be near political suicide, at least in West Germany, and would deliver the CDU (and moreso the CSU) material for thirty years. The only scenario of something like that remotely possible, from today's standpoint, would be if there was a SPD-Grüne minority government relying on support from the Linke, which would be exactly as unstable as it sounds, and crash after three months because whoever leads the Linke at that point becomes either bored or outraged that the government does not immediately transform Germany into a Stalinist dictature.