Electricity prices in the UK (and most other places) are set by the marginal unit, which is the most expensive unit that needs to be turned on to meet demand. All other generation for that time period gets paid the same price. The marginal unit in the UK is usually gas, hence the sensitivity to gas prices
As users are then paying £90/MWh for gas, does the excess £50 go to the government or to the wind far owner?
However, notice two further considerations:
1. Such contracts eventually expire. Exactly when varies. But the wind farm is still there, just now the energy price all goes to the operator.
2. Older government subsidies were not CfD. Ten years ago if you built a wind farm you got a direct subsidy. The CfD schemes come into existence from about 2014. They're one of a small number of good ideas the Tories had. They're in line with Tory ideology, but they also actually make sense in the world that actually exists.