I can say that those mechanism implemented into bitcoin will help itself from collapsing. The difficulty will prevent the miners from mining but it may make bitcoin rarer a bit due to its difficulty (full speculation). However it can sure that halving will decrease the quantity of bitcoin but increase the value which will keep mining profitable and still attract many miners. All those three have some relations and it will help bitcoin survive
The difficulty has no effect on the rarity of bitcoins. The money supply is predetermined.
The halving does not decrease the quantity of bitcoins. The quantity of bitcoins is always increasing as long as the subsidy is more than 0.
well sorry for my opinion about difficulty, like I have said "full speculation"
. About the halving part, I mean "quantity" is the supply per block which makes people feel there will be less bitcoin or rarer. It's about feeling which makes the price higher because the amount of bitcoin is predetermined like you have said