Does a helping verb always have to be paired with another verb?

Answer 1

Fundamentally, yes: That is the definition of helping verbs. However, two English verbs, "be" and "have", are both normal verbs and helping verbs and can be paired with themselves, so that a sentence may have only one root verb in two distinct words, one of which is helping and the other of which is not. Note that the words need not necessarily have different forms: In the sentence, "The prisoners had had no food since morning", the first instance of "had" is a helping verb, specifically helping form the past perfect tense, but the second instance of "had" is not.