Merkel running for 4th term

[True Federalist (진정한 연방 주의자)]

Supposing that both the FDP and the AfD manage to just pass the 5% threshold and that Merkel only needs one of them to form a government, which would she likely prefer, or would she try to take both so as to have a more stable government?

[True Federalist (진정한 연방 주의자)]

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?

[True Federalist (진정한 연방 주의자)]

You already have Die Linke.

Lafontaine & Co never managed to turn Die Linke into a Left SocDem party. It has too much bagage and its very existence blocks the advance of a credible leftist alternative.

Granted, the most recent vote share maps for each party that a quick Google found for me were for 2005, but it looks like the Greens fill that role in West Germany. What stands in the way of a Green/Left merger? Personalities or something more substantial?