@matigo I don't think Hong Kong's power grid is significantly tied to China's…haven't checked on that though.
It's actually that mentality that's why I have no intention to invest in property in Hong Kong (read: buy any at all): come 2047, all bets are off and I suspect there'll be a huge re-distribution of wealth to other cities.
For now, if China directly intervened and tried anything of the sort, one hopes the US and UK would intervene.
The "one country two systems" is quite amusing: a group of protestors set fire to a portrait of Xi outside one of the People's Liberation Army bases about an hour ago, yet the PLA comprises only troops from the mainland, so without special authorisation they couldn't come out and do anything about it.