1. As already noted by other posters, the decision to decommission these plants was made years ago.
2. As a consequence, the plants are in no shape to be run much longer without major refurbishment, rehinring and training personal. Also, the fuel rods are basically spent, new ones would have to be ordered and manufactured which takes quite some time. Want to guess where most fuel rods came from? (spoiler: Russia)
3. Yes, running them longer would have saved burning some coal which would be good for the climate.
4. They wouldn't have saved much, if any, gas burning. Gas power plants are "fast" plants, vs. nuclear plants, which are the slowest to change power output. Nuclear power plants consequently cannot replace gas power plants. On top of that, there are a lot of combined electricity/heating gas plants. They cannot be replaced by nuclear power either.
5. Electricity production is just a small fraction of gas usage, the biggest part goes to private home heating and of course, industrial usage.
So, yes, bad timing. Woulnd't have been a problem but for Putin attacking and utterly destroying parts of the Ukraine. But as things are, the best way to deal with is, to press forward with renewables instead of sinking more money into nuclear. (By the way, the real crisis is that only 50% of France nuclear powerplants are operating. Between heat and repairs, French power supply is under much greater pressure, actually often enough supported by Germany)