Glendening has been up over Callahan because every forward who has missed a bunch of time except Alfredsson have been centers, or wings who can play center when needed. If they needed a 4th line winger, I'm sure Callahan would have have his chance.
The Wings are loaded with guys who project to be solid to good NHL players. Up front they're lacking top center depth though. If Jarnkrok doesn't develop into a top line guy, they'll have to find one in trade or free agency. Jurco could easily be a 25-30 goal guy, Mantha will either be a stud goal scorer or complete bust, depending on how bad he wants it. Sheahan could have a Dan Cleary type career where he's a 40 point guy capable of playing on any line. Pulk could be a 25+ goal a year sniper. Callahan is one of those guys who will do whatever it takes to win, I think he's going to be a hell of a checking line winger. Glendening is probably going to be an ok 4th line guy/reserve forward. Ferraro has speed and works hard, so he should have a decent pro career, but he's probably going to top out as a 4th line energy player. The other guys are farther out, but I'm not ready to write Frk or Tvrdon off quite yet, and Athanasiou is looking like a potential stud with good size and excellent speed. At the very least he should be a high end checking line guy. Janmark has picked up his scoring pace in Sweden, too, and there are a few other guys with a decent chance of being NHL players.
Defense is even more loaded. Sproul and Ouellet are potential top pairing guys. Backman and Marchenko project as solid to good second pairing guys, and Jensen could be a second pair guy too. I'm not high on Almquist, I think his size is going to limit him far too much at the NHL level, unless he finds a team that wants to use him as a PP specialist with limited even strength minutes. McKee, McNulty, De Haas, Nedomlel, and Wheaton are all big bodied guys who could be decent 3rd pairing guys.
Add all that to the younger guys who have established themselves and the Wings look like they should continue to be in top half of the NHL for a long time.