I think you overestimate how much companies care about their existing employees. If firing 90% of them is significantly more profitable that’s what their going to do. Solar is so cheap largely because it needs very few workers per GWh so they can fire people.

I personally doubt Fusion will be significantly cheaper than Fission let alone coal any time soon. But, if it happens their not going to care about their workforce. That said, fission > fusion isn’t going to require more training for most of the workers. In many locations they would both have identical cooling towers for example.