I would hope by 2140 renewable energy would be exponentially cheaper than it is now. It would definitely be a bit of prisoner's dilemma for people to keep it going, but everyone who holds BTC would have an interest in maintaining its value by processing the transactions. I'm not sure how much I believe Bitcoin will still be around in that long. It's certainly possible, but even global companies with deep rooted brand value do not often last that long, and crypto is an intensely competitive market right now.