Some predict that after halving and no price increase some miners could turn their machines off and hashrate could drop because of that more or less significantly. That would be ok but bitcoin difficulty adjusts every 2016 blocks so miners who are still mining would have more work to be done to solve a block than it should be for a hashrate like that for quite a long time (normally 2016 is 2 weeks and with lower hashrate this timeframe grows). This would mean larger time between blocks which in its turn would mean more transactions waiting in line to get into the block which could lead for confirmation problems which could decrease the price which will make it unprofitable for more miners which will turn their miners off and there you go - "death spiral".

However some say that that's not going to happen because either price would increase thanks to increased scarcity or because of press covering halving event or simply because miners rent their electricity ahead of a time and a) they have no choice but to mine because they already payed and b) they have made million $$ investments into mining and should have foreseen this situation already.

I have no idea who is correct, so I'll just grab some popcorn and prepare for fireworks