I don't think Amy will leave Parks and Rec. The likely scenario is NBC canceling the series after it gets to approx. 100 episodes due to the low ratings it gets. Which in the grand scheme of things it may not be bad.
Like I mentioned in The Office thread, if The Office ended after 100 episodes we would be wanting a movie or spinoff, or certainly more open to it than a Schrute Farms one. Two and a half seasons later we just want the show to end.
I think The Office started to decline when they came back after the strike. The latter half of season 5 and all of season 6 were pretty poor. Season 7 became good again when Holly came back all the way to Michael's last episode. Now it's just plain awful.
The later half of season five was arguably the show's best batch of episodes outside season two/three. The Michael Scott Paper Company brought some life back into the series.
The show's decline happened in season six. It had some good episodes, the highlight being Jim and Pam's wedding.
Introduction of Gabe.
The just sad unfunny episode of Scott's Tots.
The Mafia episode.
The over the top Delivery episodes of Pam and Jim's baby.
Michael dating Pam's mom was over before it even started.
Episode 120, New Leads, was when The Office died. Michael and Dwight fighting in garbage against a green screen. Horribly not funny.
A very weak season finale, The Office season finales always left you wanting more and this and season seven's did not.
Gabe.