Proof Of Work is solid.  Bitcoin will be just fine.  Chill peeps.

"Bitcoin runs (only) on stranded, excess energy, generated at the edge of the grid, in places where there is no other demand, at times when no one else needs the electricity.  Retail & commercial consumers of electricity in major population areas pay 5-10x more per kwH (10-20 cents per kwH) than bitcoin miners, who should be thought of as wholesale consumers of energy (normally budgeting 2-3 cents per kwH). The world produces more energy than it needs, and approximately a third of this energy is wasted. The last 15 basis points of energy power the entire Bitcoin Network - this is the least valued, cheapest margin of energy left after 99.85% of the energy in the world is allocated to other uses." - Michael Sayor @ michael.com