Economic costs of switching are always higher than maintenance costs. Solar can totally be good enough to stand on its own while not being good enough to justify de-commissioning perfectly good power plants.
thats like saying a stone wheel would be good enough
if we didn't have pneumatic/michelin tires
anything is good enough when its the only option
No, it really isn't. If it costs more than it generates, it's not good enough. That's why the power plants were built as they were in the first place; a lot of them date from when a solar installation simply couldn't pay itself back, ever.