....can we still talk about them?

Also, if a provider delists and then a reviewer puts up a review, does the provider have to come back and keep taking themselves off?

If TER delisted the provider. I'm guessing that they would not allow a new review (if they catch it). If the provider delisted herself, TER may be even less likely to catch it and the provider would likely need to request removal of new reviews. As far as discussing delisted providers, it probably depends on the reason for their delisting.

... found at the top of every Discussion Board:  

"Discussion of delisted providers/agencies is not allowed (except for rip offs, ROBs, etc)."

Sometimes a discussion will stay up for a bit, but TER seems to always catch it and the thread disappears.

The answer is no. That rule is made clear by TER.  

To your 2nd part, she would need to request that with TER if in fact it is her wish. The lady you're asking for probably already knows this, or at least knows how to reach out to TER support and ask for herself.  

Curious inquiries...
 

1) No, although TER may not catch it right away
2) It is not the provider's responsibility to keep checking for reviews (although she may choose for reasons of her own); that is up to TER.