That's always the risk we have to take it pays off more often than not, even when it doesn't work like in Kompany's case it's usually quickly remedied.
With that particular case though I feel it was mostly out of our hands, Kompany left quite out the blue (no pun intended) to player/manage his boyhood team... I think that possibly caught us really off guard and we weren't fully prepared to replace him with anyone second rate, it was kind of last minute we expected him to be here longer unlike the others where we were fully prepared.
I do get your point he's a fantastic player Riyad with very high qualities, he won't be easy to replace but we're constantly evolving, Pep might think the defensive demands needed by our new system might not be to his strengths, that's not to say he didn't work hard tracking back a few times last season once it was implemented.
Pep though is a ruthless manager if he's sensed that we can move Riyad on I trust that judgment, personally I'm torn but I think that he might want players with more energy to quickly win the ball back... Like Phil or Bernardo or Alvarez they don't have the numbers Mahrez does, what they bring off the ball might be the deciding factor for Pep, I'm not saying it's defo the case but he's ruthless and that's why he's the best.
We should just be careful not to lose Gundogan Bernardo and Mahrez in the same summer window, this could be a serious problem but if we keep Bernie another year to cushion the blow I'm happy, if not we definitely need at least one more high quality midfield signing.
Only time will tell where our players will play next season but I can see a lot more evolving, a few surprises with chopping and changing thanks to our really versatile squad, especially with KdB potentially out a while but it'll be a good test for the lads early on.