Season 8 Changes (spoilers)
So I have watched this series over the years by starting and stopping after they become available on Amazon Prime. I only recently re-started watching starting around Season 7, and then got to Season 8, and WOW. I guess I didn't get the memo that both Rachel AND Mike were written off the show! I kind of figured that Meghan Markle wouldn't continue with the show after the royal wedding, but I never read how this would be reflected in the storyline.
Anyway, at first I was deeply annoyed by this huge change because I thought Mike and Harvey were the entire reason for the show's existence. It would be like having the Dukes of Hazzard without Luke Duke, or CHiPs without Officer Poncharello. I considered giving up on the series at that point.
However, as Season 8 progressed, I found that the storyline was compelling enough to keep watching. Robert Zane was always a strong character, so it was interesting to see him enter as a more central part. The character of Alex was also likeable enough even if not terribly deep, and Samantha Wheeler brought a new Harvey-like rival that turned out to be really quite interesting.
In the end, I found the writing was strong enough without Mike and Rachel to continue on its own two feet through Seasons 8 and 9. I actually thought that it was beautifully crafted in the way that Robert Zane in and out of the storyline while keeping him in periodically in Season 9, and also how Mike came back in key ways in Season 9 without feeling like he was window dressing (like the way Michael Scott did his appearance in the finale of "The Office").
Overall, a great series.