The leftwing bloc was never winning in 1990. Other than in 1983, the conditions in 1990 were probably the most favorable that the CDU/CSU/FDP coalition ever had. No government that just reunified Germany was getting voted out.
1994 is a more interesting scenario. I think ultimately Kohl's popularity and the credit his government was still being given for Reunification ensured that the CDU won that election. I think the CDU was going to be by far the largest party in 1994 as well. The question is more whether the CDU/CSU/FDP coalition would have had a majority or not more so than whether the SPD would seriously dislodge the CDU.
In an alternate timeline, I could imagine a CDU/CSU/SPD Grand Coalition not unsimilar to those in place in the 1960s or during the Merkel years, with Kohl staying on as Chancellor. I think he and CDU were just too popular to dislodge at that point, especially given SPD would have had to rely on a shaky coalition with PDS and the Greens in any other scenario.
So for 1990, I don't think any other scenario other than what happened IRL would have been realistic, and for 1994, I think it would have been a question between a CDU-led rightwing bloc staying in power like they did IRL, or a CDU-led Grand Coalition being formed.
I can't really see an SPD-led leftwing government taking power before 1998 like what happened IRL.
You're pretty much right here, though on the last point, 1994 was already very close and the coalition just barely won a majority. Kohl just got the exact numbers of votes in the Bundestag to get reelected chancellor.
As for 1990, however, it's interesting that many of issues Lafontaine warned related to the DDR economy later proved to be correct. Nobody at the time wanted to listen though. And I'm saying this as someone who was never a big fan of him.
That's why I think a grand coalition would have been a very serious possibility. I'm very aware that the 1994 election was very close between the 2 blocs. The rightwing bloc could have easily lost its majority. What I don't buy is that the leftwing bloc could have formed government on its own, especially not with CDU having a good 40 seats and 5 percentage points more than SPD, and with how shaky any coalition relying on both PDS and the Greens would have been.
But in 1990, nothing was preventing the right from reelection.
