A major use for Russian gas in Germany is heating. Nuclear power doesn't really help with that. The second important use is in peaker plants that go online when there is no wind. Nuclear doesn't really help with that either.
Sure heat pumps are the future. But it will take decades to replace existing heating systems with heat pumps. We still install hundreds of brand new gas heaters every day in Germany.
It may exist somewhere (especially in France, if I'm not mistaken), but it doesn't exist in all of our (I'm European) houses. Good thing that spring is coming but I don't see our houses getting converted to electric heating till next winter comes. Or maybe the hope is that Putin will fall by then or that a nuclear winter will make all these concerns obsolete, anyway.
Switching wholesale from existing gas heating is not a trivial exercise though.