I could imagine the following:
In my mind a main purpose of copying things to "tea" was to have it readily available if a discussion regarding who said what should arise. If you do not clearly anticipate this happening or the comments are part of an already ongoing discussion, I would suggest you just delete them without "back-up" on meta, on the grounds that now (and this is new, AFAIK) you could still do so latter (or even undelete them if the need arises). (So the doing so 'just in case' seems not needed anymore.)
Complete conversations should stay (chatty and obsolete or not). [Except I am not really sure how this moving to chat works, so I might revise my opinion regarding for very 'chatty' if some information on this should come up.]
Conversations that are already incomplete (due to parts being deleted) and obsolete should be deleted completely. To give an abstract example of what I have in mind (strike-out means already deleted):
User 1: I do not understand the question. As written this is clearly wrong.
User 2: @User 1, I guess p^2 is meant instead of p also, it is likely assumed p is prime.
OP: @User 2, yes this what I meant. I edit the question. [Edit gets performed.]
In this case I see I no merit at all in preserving the remaining comments, and thus they should be deleted.
I have no strong feelings regarding this, but would rather be careful regarding deletions, as the risk of upsetting somebody outweighs the benefit of having a 'cleaner' site [this for the chatty and obsolete type]. Also, as opposed to edits, these deletions are not transparent for everybody considerable more restraint seems appropriate.