What happens when bitcoin mining ends? Well...no one knows. The good news is that it won't happen for 100 years, at least according to reliable estimates. Bitcoin works via a process of mining, which makes new blocks on the blockchain, and also keeps the platform running.
There is a theoretical limit of 21 million Bitcoin, and this raises some questions about what happens when there are no more Bitcoin to mine. There are no firm answers about what will happen in 100 years where there are no more Bitcoin to mine, but there are a few ideas of ways to keep the network running.
The first is to charge a fee for any transaction. In a sense this is already the case, but at the moment, the fees that are paid result in the creation of new Bitcoin entering the supply. It would be very easy to modify the Bitcoin blockchain to take a little bit of each Bitcoin as a fee for approving the transactions, and updating the blockchain.
People worry too much about the future, and if Bitcoin is popular in 100 years, there will be a solution to keep the Bitcoin blockchain working. For the moment, we don't need to think too much about it, as it is a purely theoretical matter.