In the past when Rob was between jobs, Rex never quite ruled it out, but in looking back at his comments on the matter over the years, it sounds like Rex would prefer they forge separate paths in the NFL -- at least for now.
On defense, Ryan has an ideal setup with a group of loyal and trusted coaches. Defensive coordinator Dennis Thurman has been with him for years and isn't going anywhere. Rob's visit could have been something as serious as a consultation, a self-scouting of sorts, or it could have just been a chance for Rob to hang out and be around football for a little while. After all, he's still collecting paychecks from the New Orleans Saints.
If and when Thurman gets a head coaching job of his own, perhaps Ryan would consider Rob for a role on his staff.
This could be a sentimental decision Ryan makes down the road, too. Emotions change. He could long for the days where the two coached under their legendary father, Buddy, and maybe time will have a way of changing his mind.
While we wait, you'll have plenty of time to Google pictures of their time working together, glorious mullets and all.