- what happens after 21 million bitcoins have been mined?
The amount of Bitcoins will be under 21 million coins people round up to 21 million coins in the real world we have much less Bitcoin in circulation because a unknown amount of coins have been lost but we have probably lost millions of coins from negligence.
- What will miners do after the total of 21 million bitcoins have been mined?
There will be less miners mining blocks because the incentive will be smaller atm miners get rewarded from block rewards and transaction fees when the block rewards stop because Bitcoin is not being generated anymore miners will only receive transaction fee. The difficulty will probably drop as the miners drop. We will always have miners though because there will always be a incentive to mine for transaction rewards.
- Will the total supply be increased because some bitcoin holders have died and others have lost their private keys?
Pls your suggestion will be highly appropriate and I believe will also help other members.
Bitcoin total will never be increased I think it is possible with a hard fork but you would have no support for it. Satoshi when he created Bitcoin knew that people would lose the coins and die. He probably worked out that 21 million coins is the best amount for inflation and value but he would have known that a lot of coins will be lost.