They should never spend the base capital.I have seen forecasts from the CPPIB where they may have to start spending "some" of the investment gains to pay for benefits to retirees in the future, but never seen any time period in the future where they spend any of the capital in the fund.
That's a fundamental principle of perpetual pension plans.
Because the number of people in the plan will continue to build.From their own projections, the fund will just continue to build.
Every time you add a person the fund should grow.
It's important to note that funds "capital" isn't the same as the participants contributions.
I suggest you read a basic intro to pensions, you don't seem to understand hwo they work.