Actually it kinda did. Many episodes with them standing around while the Thinker and his wife furthered his dastardly scheme unmolested. Each season of the past few seasons have been painfully stretched out because they chose a specific formula that, overtime, intuitively becomes harder to sit still for. What they've done this season is really not unlike what they did last year or the year before. They really should give the one storyline per season arc a rest.
No, you list what you feel is possible then you create a hierarchal list from most preferred to least. That is how you develop options and backup plans. The reality this series rejects (which in turn stunts it dramatic growth and potential) is there are times when your best option is your least preferred, and dealing with it is one life's hardest challenges. Sadly The Flash sidesteps this which is why it will never rise above the rank of juvenile in its writing.
No, there are probably options, however, the meta "cure" was the most direct (A to B) therefore efficient solution. They could have lopped off his hands so he couldn't throw shard of dark matter. They could have strove to kill him. They could attempt to lobotomize Cicada. But again the series likes to make them feel guilty over things they can't control and shrug off things that they can. So far they seem to feel no guilt over capturing a murderous criminal who then escapes to kill again. Civilian lives are fodder to them so you get a certain hypocritical feel good about themselves "morality."
Crickey, you've never worked in television! I remember in the lead up to both Voyager and then again Enterprise (even DS9 to be honest) all the actors in the interviews were looking forward to the financial security the series would bring them. You work a series (hopefully a 7 season run) so you can amass that coveted "F.U." money that allows one to start picking and choosing their jobs. Actors especially will look to go the distance on a series unless there is something dysfunctional going on behind the scenes.
Also the fact several are leaving at once (2 actors and 1 showrunner so far) has all the earmarks of a shakeup because the metrics have softened. That is not to be construed as a negative on anyone. It is just the way things go sometimes.
As for their leaving, I am not cranky about it one bit. I like both characters, however, I also feel the series would benefit from a big change. Secondly, all seems to be on good terms so I hope they'll be brought back from time to time. Maybe they'll transfer to Legends final season.