We might think we can get by without the sun, and it might have been true, whilst we lived by consuming all the energy on Earth, including all life on it, but when that is exhausted, beyond being accessible by profit, as it is becoming right now, we have to start looking to the sun, to provide the energy we need via solar energy technology which is coming to maturity now, so we might be more inclined to admit, the sun is very necessary for life on Earth, at least as we know it.

This is not an assumption, it's something that can be observed, just by looking at how nature works, and how we work (Two different, opposing things to date), using the tools of formal multidisciplinary systems Engineering.