ETH PoS — remaining long-term risks?

Everyone is talking about 2.0 merging in Q1 2022 (or even Q4 2021), mining difficulty increasing, and PoW being history shortly after.

1) Is anyone following the core team discussions and knows how confident people are that PoS can fully replace PoW? Is it just a question of "when", or is there still some "if" / "how" left?

2) What are the most feared/realistic risks — e.g., pre-merge angry miner 51% attacks, validator collusion (MEV), long-term centralization of power, trust in volatile token collateral vs. "tangible" energy cost, etc.?

3) What would a rollback look like if the switch was flipped too early? Is there a full rollback scenario?

4) Bonus / off-topic: any hypotheses on where all the GPU hashpower will go if PoS takes over in Q4/Q1?

Thank you.