From a legal perspective, as far as I understand it (but I'm not a lawyer):
What would actually happen if Steemit shut down the website, and Steemit Inc. totally powered down and wanted out with as much remaining funds as they could get their hands on?
They'd be in their rights to do so.
What consequences would there be?
None, besides paperwork I'd assume (if that's a consequence hah).
What positives would there be?
Hard to tell, positives for the blockchain might be that it's now community controlled, and we could attempt to actually make some progress without getting blocked by a corporate roadmap.
Would any witnesses remain capable to run the blockchain?
Yeah - the blockchain would be fine. Steemit Inc could pack up their bags and shut everything down that they operate, and the blockchain would continue on. The witnesses are completely independent of Steemit Inc, and if they were to sell their tokens, out of their control.
How much does community retaliation efforts or good faith in Steemit Inc affect this potential outcome? In other words, is there anything we can do to sway the outcome?
Honestly, I don't know. That's part of the reason I am considering leaving.