Nobody is taking that chance. At the moment. But if Russia shows that they are willing to use their nuclear weapons to the point that it becomes believable that they will do so anyway then we are in completely uncharted territory. Note that this war isn't over yet and that Putin has threatened multiple times now more or less obliquely that he would not hesitate to use nuclear arms in a first strike situation for whatever pretext he seems to think is enough. This was then later walked back again by other Russian functionaries but the damage is already mostly done: Russia is no longer believable, and apparently nuclear first strikes for pretexts are on the table.