Well you know it's time to let go when the showrunners themselves start mocking the show. This show should have ended once upon a time ago with season six. The problem was that season seven hit a high point with its 4th episode, that focused on Belle and Rumple (not to give any spoilers away), and they never came remotely close to matching its quality. That episode, along with the 2nd ep, were the ONLY good episodes in the entire season IMO. Plus with those endings, guest spots, and regulars out of the way, the 7th season was free to primarily focus on its entirely new cast and characters, but when you compare it to what we had before it quickly became a snore-fest that rivaled none other than, wait for it... Snow White's very own sleeping curse. You never really connect with any of the new characters.
The show tried to make us care about the new characters and, given time, maybe we would have. However, since it's been canceled, it made all the work and time spent on it a bit pointless. Season seven needed to be bolder and it needed to make a clean break from everything that came before it because comparisons to the established characters who stuck around didn't do it any favors in the end, and ultimately was one of the reasons why season seven sucked...
Almost reminds me of the last two seasons from Stargate SG-1 (just not as engaging); no Jack O'Neill as a regular, no chance in hell at holding a candle to seasons 1 thru 8. 