Pep will certainly strive to bring Manchester City back to the title next season. If City fails again, Pep's reputation will suffer somewhat. Manchester City does appear to have made quite thorough preparations in the current transfer market. However, I still think De Bruyne's departure is quite unfortunate. I don't think the player brought in to replace him will necessarily be on par with De Bruyne. So, Manchester City could start to lose their strength in one area. But I think my concerns are overblown. Pep certainly knows what he's building at the club.
I think your concerns are not overblown. Given Manchester City's inconsistent performance last season, it's understandable that we're unsure or worried about this team in the new season. Furthermore, De Bruyne's departure was quite difficult. But we also have to remember that Manchester City went through a season without De Bruyne, when he was sidelined with a long-term injury. And yes, Manchester City were fine at the time. However, when De Bruyne returned, Manchester City improved even more. But Manchester City didn't dare take the risk of keeping De Bruyne, who is always prone to injury. So, in my opinion, letting De Bruyne go isn't a bad choice. Although, it will certainly be quite difficult to find a player who can match De Bruyne's performance. But I'm sure Pep has a solution.
Currently, Manchester City has successfully brought in six new players. And the number is likely to increase, as I'm sure Manchester City isn't finished in the transfer market yet.