They're already dropping plenty. Ars Technica reported[0] a few weeks ago that nVidia is currently struggling with a stock surplus, rather than deficit, and Amazon UK has several RTX3070 SKUs shipping at MSRP or thereabouts.

0. https://arstechnica.com/gadgets/2022/08/nvidias-excess-inven...

Potentially after the chip and supply chain crisis

The switch to proof of stake is not exactly abrupt, it was,discussed and planned well in advance. I bet the video card makers must have been preparing.

Unlikelly. Miners are still mining other crypto. Some believe ETH is worth nothing now that it is not PoW anymore, so they are choosing other crypto to mine.

I wouldn't wxpect people to atop mining. But will as many people purchase cards specifically to mine?