I actually enjoyed the climate of the fandom much more between Last man and S&R, because there wasn't as much petty infighting about what episode sucked and who was wrong and what 'ship would ruin fandom blah blah blah.

I dunno if there will be a drastic decrease--I think it'll very much depend on the way it ends. If it ends with any subtext at ALL to follow up on, we'll be on a high for quite a while, wrapping that up in our various ways.

To be brutally honest, I think some people are worried about the BNFs whose attachment to fandom was tenuous at best pre-announcement. Knowing that some of one's favorite authors might be going 'ah! there's the excuse I was looking for. BYE' is enough to get many worried.