I know that mining is not profitable at all due to rising difficulty caused by "mining-noobs", losing a lot of their money.
If the block reward exceed the cost in electricity and roi is impossible then will some miners (with lower hashrate = lower probability to find the block) shut down, and then will the difficulty go down, and then will roi be possible for others.
The system will self-adjust to a level where there is a profit for the miners. You won't see this happen in the next few years. Because most miners dont think rational like that. They think like: Bitcoin is going to rise in value, so it makes sense to mine. But they don't see that their revenue would be significantly higher by a direct investment in btc.
I think you are underestimating the intelligence levels of miners... Sure you can find single cases that support your statement, but the majority of the network is commercial now.
I am sure there are irrational miners out there, but I don't
most miners are irrational.
However, I am quite sure it is not just a few single cases.
For example, if you take a look at cex.io, you will find people buying 1 GH/s mining contract for 0.043+ btc.
And, the GH/s price is pretty stable even after the difficulty readjustment.