There are only 21 million total bitcoins that can be mined, what will happen if all bitcoin is already mined?
According to research if bitcoin reach its limit, it will be disappear but it doesn't happen already so don't worry. I think devs will solve the problem to extend.
One of the options now is to develop bitcoin. In the future there is an issue stating that there is a new type of bitcoin that will be outstanding. But it is still limited to requests from several communities only. We'll see later, but I still like the bitcoin that exists today. Changes can sometimes lead to good, but sometimes can make things worse.
No. According to what research? Bitcoin will still exist when all Bitcoins are mined and the developers don't have to do anything about it.
Miners will keep mining and getting paid from the transaction fees of each block, which will be adequate due to the huge amount of transactions assuming Bitcoin also scales on-chain.