Hi,
Firstly, sorry if its a really stupid question.
for what i know:
Digital currencies can be easily doble payed (using same coin to pay two transactions)
To aid this, all transactions are held upon confirmation buy all the mining machines looking for blocks.
These miners are rewarded with newly generated coins that get produced.
Difficulty levels adjusts in order to equilibrate the mining of coins which also half every 4 years.
So the question is: when the number of bitcoins reaches 21 millions and no more coins are produced,
will all the bitcoin system rely on non-rewarded donating miners in order to not go wrecked?
The miners receive both transaction fees and receive newly minted coins; once all coins are minted (sometime long after we're dead), they'll be paid only in transaction fees. The question is, how many miners are required to strap the system down? Hopefully it matches up well with how many people will be using Bitcoin by the time the last coin is minted.