This pipeline has an annual capacity of 55 billion cubic meters. It's the same capacity as the Nord Stream 1, which is already in operation. If Germany was truly meaning business, they'd stop Nord Stream 1 the moment Russian boots enter Ukrainian territory. But let's leave that aside.
55 billion cubic meters translate to about 0.6 billion MWh. The price today for natural gas Dutch TTF futures is EUR 78/MWh [1] , so that translates in about 40 billion EUR per year. It has been as low as EUR 13 and as high as EUR 165 over the last 2 years. It's quite likely that Russia would make a profit even at the lower range, so the 40 billion EUR/year is pretty much pure profit for them.
[1] https://www.theice.com/products/27996665/Dutch-TTF-Gas-Futur...