I agree with this. I don't think there is a single character who can replace Rick, instead, there will be others who will try and step into the role of Rick, but they will never be Rick. Hopefully, this opportunity will allow other characters to propel the story in a way that never would have happened if he was still there. Only time will tell. The funny thing is that Lennie James was brought in (apparently) to save Fear the Walking Dead, and all his character ever does (for the most part) is gripe about not wanting to be the leader, but it will be interesting to see what the future holds for TWD and whether or not the show can flourish in Rick's absence. Otherwise, TWD may need it's own Lennie James impersonation to save the day.
I do have to admit that this 4th season of Fear the Walking Dead is more interesting than TWD, so far.