Translation:Torg is falling.
Using present or past tense, or even future tense, is fine and can only be limited by context. Since this sentence has no context, it is fine to use the past tense, but you have failed to include some indication, in the English translation, of the continuous aspect represented by -taH. The suffix -taH indicates an ongoing aspect to the action and your suggestion, "Torg has fallen," describes a completed action. A better past tense translation of this sentence would be, "Torg was falling." And a good future tense translation would be, "Torg will be falling."