I don't think you can get viewers back with the promise of big story lines to come. Negan was overhyped as being an amazing villian with amazing story lines, but has fallen way short. The whisperers don't really excite me, people who have no idea about the comics will be even less interested.
I actually missed the 4th season. I watched the first 3 seasons on dvd then had austar put on at my new place just in time for season 5. But even though i enjoyed the walking dead, i just couldn't watch season 5 without watching season 4 first. So the hope to get viewers back for an exciting season 8 will be hard because many don't want to sit through a dull season 7.
The show is in a downward descent, the glenn death fake-out ( only to kill him anyway), the slow build up to negan, then the way the cliff hanger was handled, the incredibly slow pacing issues, filler episodes ( a tara centric episode?) And basically the show becoming repetitive means that they have to make huge changes just to keep the viewers they have