If he's really retiring from anything football then I didn't see him coming back again as a player but rather could back as coach or take any football related task.
Indeed Toni Kroos is a player I admire so much in the field of playe especially during his stay at Bayer Munich ,his incredible performance and contribution to the team's mid field would never be forgotten when it comes to football.
I don't know where did I see that Toni Kroos will join Real Madrid this time as a manager for the young or something like that. I don't know if someone saw it or it was just a rumour? I am pretty sure that Kroos will take the path of the others and start a training career with all the required certifications. Although we have many managers right now but there is still vacant places for many.
This can be a possible situation because not a few legends at a club immediately devote themselves to the club they previously defended even though they are no longer players there. We can take the example of some great players like Cech even though he has now left Chelsea but it does not rule out the fact that the Abramovich era Cech's role as a successor behind the scenes at Chelsea needs to be applauded. This is possible for Kroos but indeed things like this cannot be decided quickly because after all, management must see the potential in the end because even though they are legends but still in situations like this there is no special privilege to bring legends to be part of the club's internal management because it cannot be done unless the person is really qualified.