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.