Thanks, Matthew and Nagaraj. The present tense verb "is" in the sentence, "However, this great Indian tradition is on the wane due to
some selfish, reprobate and untruthful preceptors," does make it sound like the reference could be to contemporary preceptors. If, however, the Sanskrit announcement letter is the original one and the English letter is only its translation, then we do indeed have the past tense verb āsīt, "was," in this sentence. In that case, and without further clarification from the Rāṣṭriya-Saṃskṛta-Saṃsthānam, we would have to assume that they mean by "some selfish, reprobate and untruthful preceptors" those such as the Buddha, whose followers Śaṅkarācārya is depicted as defeating.
Best regards,