In mining you don't loss coin only the amount of money you spend to buy the equipment, except that nothing more and if you a good miner you get the money within one month
A miner can run at a loss if they do not have enough hashrate, yet they are paying for expensive electricity, a miner has to ensure that their expenses would not exceed the possibility of the revenue they can make, that's why it is better to join a mining pool rather than solo mine when you do not have enough resources. A good or bad miner just depends on how much hashrate you or your pool can generate, that is what increases or lessens your chances of finding the next block.
Bitcoin mining is not so easy right now and it is It's a matter of time for every block mine.
There is no end to BTC blocks, BTC transactions will always be confirmed and added into a block, what is going to stop is block rewards, and that is after every BTC has been mined; but that's not going to stop BTC mining because miners would start receiving incentive from transaction fees.