Is it still possible a red-red-green coalition?
Not really at all.
Wouldn't take a month no matter what happens. Per German law, if no Chancellor candidate has been elected by a Parliamentary majority after two weeks, there's one final vote, then the German President picks between making the plurality winner of that vote the Chancellor or hold new elections. And Germany has very strict requirements for a no confidence vote so Merkel could easily manage a full term minority government; a majority of Parliament not only has to vote her out but there also needs to be a majority agreeing to her replacement for her to be removed as Chancellor.
A red-red-green coalition most definitely wouldn't be considered the will of the people because the majority of all three of those party's voters almost certainly would oppose such a coalition.
This is basically comparing apples and oranges.
