Fusion will obviously replace fission if us monkeys can figure it out.
The cost of a dyson ring would beggar the entire planet for at least a milllion years. It is simply infeasible until energy to matter and matter to energy conversions hit 95% efficiency.
Renewables will easily replace fossil fuels, and can already economically do that in some cases.
As to fission/fusion, You seem to be unaware that the sun is a giant fucking fusion bomb, only the distance we have from it's multi-billion year continuous explosion and our atmosphere keeps us alive.
The technology to gather the solar fusion energy impinging on our planet improves daily, it's a race between the gathering tech people and the local fusion tech people, and so far, the gathering tech people are winning.
The future may well be different, but right now the best fusion generator we have is exactly 1 au away and we need to (and are, continuously) improve the tech we useing to capture that energy.