What if we also solve fusion and build a Dyson sphere and farm unicorns for automotive fuel? It seems somewhat unreasonable to assume that our energy usage is

What if we also solve fusion and build a Dyson sphere and farm unicorns for automotive fuel? It seems somewhat unreasonable to assume that our energy usage is going to exponentially increase due to as-yet-unforeseeable future needs and at the same time assume that we'll completely fail to find additional energy sources in the same timeframe.