Freezing to death this winter because your source of fuel oil is now your geopolitical enemy seems like a more pressing problem than the tiny amount of waste 3 plants will generate decades from now.
The decision to keep these 3 plants running or not is not about the waste, but about the fact that they were planned to shut down for years now, and there is some real hurdles to reversing that now. The impact of keeping them on is also rather small. The effort and money is more effectively spent elsewhere.
If they would be easy to run longer, I would be all for it. But big money is better spent into reducing the gas dependency overall.