It was not an easy decision and I fully respect everyone's point of view because I shared the same concerns. But we had to make a decision and bear the consequences.
I'm OK with all the witness vote removal I got, including yours. This is truly what DPOS is and that's a good thing that people remove their witness vote if they disagree with what their representatives are doing.

Do you know if anyone is now watching to see if Sun is powering up any other accounts?

Yes, the blockchain is under close surveillance;)
This is how we noticed significant STEEM movements on some accounts before the acquisition of Steemit by Justin Sun, without knowing what was going on behind the scenes.

Is there any contingency for that scenario?

Yes, because the Justin/Tron Foundation has a load of money. No, if it's not worth it.

What are the Witnesses prepared to do if he were to do such a thing

Nothing. The softfork is not against Justin Sun or any wealthy enough investor. It is only about pre-launch ninja-mined stakes of Steemit accounts.

... or actually responds in some fashion that is either considered insufficient again or acting in bad faith?

I do not agree to leave the softfork applied forever. Shall he behave like Snaky Ned, I may revert my nodes to prior-SF version (i.e. unapprove softfork) and decide whether I leave the platform or not.

Regarding witness communication with the community, we already did some at the Curation Corner forum hosted by @shadowspub yesterday. I hope she will publish the recording soon.