Bitcoin cannot provide loans.
Lets say all ~21million the BTC have been mined by Bob.
Alice wants to purchase a house for 21million BTC.
Bob lends the 21million BTC at 5% PA for 25years.
How is the interest paid?
this is a unrealistic scenario, it's like saying if someone hold all fiat currencies he can't pay the interest anymore, as long as there is no printing, so i think you are insinuating that because the supply of bitcoin is limited there can't be loan if such unrealistic situation appear? it does not work in that way....