For such measures: continuous dormers on both sides and an additional nearly 50m² extension, even I would consider demolition and rebuilding. With these construction measures, you are also exceeding 50m² of living space renewal in total, and all requirements of the Energy Saving Ordinance and the Renewable Energy Heat Act for new buildings apply.
The plans show a wall thickness of 24cm everywhere. That probably can't remain as is. Given the amount and the planning, probably only the walls—and even those only partially (not even the roof structure yet)—will remain. I would rather demolish everything except the basement and build up anew from there.