There are various meetings throughout Germany taking place by members of the SPD Party (way beyond the group in Berlin), and their open criticism of the coalition agreement draft is being picked up by the news media.
It's safe to say that 'they' (the lesser people in the party) won't approve the coalition deal unless more is added (the immigration pieces aren't enough in their opinion....more on the civil insurance deal...etc).
The odds of a renegotiation maneuver by the SPD leadership? I'd say it's better than a 90-percent chance that an additional week of talks will occur. The 28-page document will likely expand out to fifty pages minimum.
The odds that Merkel's CDU will readily agree to things? Your only two other choices are a second election or to run a minority government. If you add the CDU-CSU team, with the FDP numbers, and even the AfD folks.....they would hold the majority of control in the Bundestag. Whether you could depend on the two other parties to vote in your direction is a question-mark. Another election? One might suggest lesser numbers for both the SPD and CDU, meaning an even weaker outcome in such an election.
At this point, if they admitted failure by the end of January and opted-out for an election....it would likely be the end of March before it'd occur.