Tseng wasn't necessarily killed. He was wounded, but still alive enough to make it back to the entrance to the Temple, where the party finds him, and he's still alive at this time.

Also, in the Japanese script, at Icicle Inn, Elena blames Cloud etc for hurting Tseng, not killing him. Presumably, she found him and got him to safety, and assumed his injuries were inflicted by our heroes. Logical, since she knew they were all at the Temple of the Ancients at the same time.