I don't actually see the disaster at all. Prices are staying low for millions of people already living in the city. Yes it's a pain for people who move but it might very well be a worthwhile trade-off.
However the real long term point is made at the end of the article.
>"The biggest question is whether this episode of left-wing populism has damaged confidence in Berlin’s real-estate market permanently. If investors fear that local property rights will be put at risk in every election, they might stop building houses in the city at all."
This isn't a disaster, this is what needs to happen. Drive down the property market, reclaim the housing stock, turn it into mixed income public housing, which is exactly what Vienna did when the Social Democrats took control of the city in the early 20th century. Today most of Vienna's housing is public housing, and it is considered one of the most livable cities on the planet. Driving the landlords and real estate companies out of the city is only a disaster for the professional rentier class. The only problem Berlin has right now is that it hasn't gone far enough.