But this then brings the question back (atleast for me): What happens when all coins are mined? I just looked it up and it's already >80% mined. So if miners would leave the pool and then suddenly (suddenly might even be a long period of time here, I don't know to much about bitcoin) all coins are gone. What happens?

Edit: What just got to my mind is that we will never gain more bitcoins then those 21 million, but we surely will lose them (people lose they keys, die, whatever). Will the price go up to "infinity" or will it suddenly drop to 0?

According to [1], in 2140 each block will give 0.00000042 BTC (big guess based on mining trends). The reward per block goes down as the number of remaining coins reduces.

This introduces a very unstable system. If the price of bitcoin doesn't (double + increase with inflation), as the block reward shrinks, the rewards will become useless.

1: https://bitcoin.stackexchange.com/questions/10486/when-will-...

Theoretically, transaction costs (will) pay the miners.

Exactly. And a drop in hash power and difficulty, which have a lag between one and the other, enables miners with more expensive operations to enter. Of course, they suffer when the reverse happens..but such is life.

It was interesting when Monero did their first hard fork for "ASIC resistance" reasons.

I happened to be paying attention that day, and there was a brief period where the network was small because everyone's miners couldn't participate until they were updated. My little single-GPU miner was suddenly rather effective because I had it back up immediately while the difficulty was very low. These days I don't bother turning it on, but when the scheduled forks occur there's probably still some opportunity for the little guys.

What happens when the expenses to open new operations are too high even for the largest miners?

What happens when mining slows to a stalemate?

A hard fork that resets the mining difficulty would be the only option then I think.