I was wondering about an alternative ending of this game, since a nuclear explosion doesn't seem a happy ending.
So I disassembled the game and found that there is no alternative ending
But I found that there are some text screens inserted in the ending, only shown if you run the game on a japanese MSX. They explain the nuclear explosion, and show the game staff. This is the translation of those screens (credits of translation goes for Gunkan):
"Afterwards, when I was investigating the materials about Ushas that
the Assistant Professor Atley had newly found, it was made clear that
the statue of Ushas was a nuclear bomb fuse that the ancient
civilization had developed.
It's switch was the jewel, and to prevent from using it, it is said that
the jewel was split into four pieces, and were scattered
amoung many places and sealed"