if googlebot chooses to render the page, which is - in my experience - not always the case (sometimes the fb stream got indexed, the spage got found for it, the other time nothing, sometimes a page that got found for a comment then lost the comment again, pretty random stuff). but yeah, if you think it's worth it you can still fetch the fb comment stream and put it below the fb plugin.

What if you want to enhance your local search to comments? e.g. "find entries which have X in one of the comments", or sort stuff by number of comments - anything really? You do nothing, because you can do nothing. You're basically screwed because you thought the input of real people on your work was fit to be outsourced.