You're reading too much into it. Not being present would not mean "because he's a corpse and mutated, lol". It means Tyr wasnt around to see Loken's fall from grace, nor the subsequent events that eventually led to our victory over Yoggy.
Found some blue posts regarding the topic:
Q: What's the relation between The Order of the Silver Hand, Tyr's Hand (City from Lordaeron region) and Watcher Tyr (from Ulduar)?
A: Long ago, on the continent that would eventually become known as the Eastern Kingdoms, a small group of creatures struggled to survive, using the limited supplies provided to it by parents who had just abandoned their children on an unfamiliar shoreline. These creatures, eventually called "humans," would occasionally take to gathering around a fire whilst trying to read from scrolls telling of ancient heroes and leaders – tales from the civilization that had cast these creatures out. One of these scrolls spoke of a great leader, a paragon of order and justice, who sacrificed his right hand in a fight against an unfathomable evil. Although it was within this hero's power to fix his hand after the fighting had ended, the hero instead chose to replace it with a closed fist made of the purest silver. In this way, the hero impressed upon those who followed him that true order and justice can only be accomplished through personal sacrifice. This hero, who slipped into memory long ago, went by the name of Tyr.
Q: Building off that- whatever happened to Tyr?
A: The watcher Tyr was not in Ulduar when adventurers finally freed the titan city from Yogg-Saron's influence. If anyone knows where Tyr is now, he or she isn't speaking up. (
http://blue.mmo-champion.com/topic/1...swers-round-1/)
Q: As a keeper of Order, he's...kinda missing the ball here.
Wowwiki suggests that maybe he went to Uldum in Tanaris, for whatever reason. He seems to be associated in part with the Vrykul, as he has a terrace named after him in Utgarde keep. He has no place at all inside Ulduar that could be dedicated to him, so...where is he?
A: Tyr went on a path he felt he must follow... whether or not we learn about this journey remains to be seen. (
http://blue.mmo-champion.com/topic/5633-where-is-tyr/)