In OTL, an event that still makes me giggle is that once the dye was cast, even Hoenecker voted in favour of the motion to remove him from power, so ingrained was the habit of voting with the majority.
ITL, I could see Photos and video footage of NVA Troops firing on protesters hitting the international news big time. At which point, Gorbachev would publically AND privately condemn the actions. I could see the BRD requesting a motion of condemnation in the UN, getting it and potentially the Soviet Union either abstaining, or actually voting in favour of it.
While the West German military would not take action, private individuals most likely would. Symbolic protests to start with - cutting the wire at border posts while Border gaurds look on from both sides. Mass walk overs, not in Berlin, but elsewhere, DDR citizens, while DDR border gaurds turn a blind eye, just walk over the border. What goes back over the border would be blacker than midnight in a celler on a moonless night with the curtains drawn and your eyes closed, and probably routed from Langley via Bonn.
It would be a mess of dystopic proportions. Eventually, the government would fall, either to a revolution or an internal coup and Hoenecker would either end up with a long drop on a short lead, or placed against the nearest wall.
No BRD Invasion, military, civillian, humanitarian or otherwise