We'll take Kimmich for him.
Gutted to see him go, but he'll be 34 by the end of next season and I think the CL win is kinda mission accomplished for some of the older players, who might be looking for a new challenge. The main worry is that we've already got a long list of players that are 'leaving' this summer and I didn't expect him to be one of them.
As for the whole four CB thing, yes it's worked well this season, but ultimately, we need tactical flexibility. If four CBs becomes our only option, then that's a worry. So he'll definitely need replacing with a proper full back imo.