According to the figure with the cycle, both Ammonia and Ornithine feed into OTC to become Citrulline. Thus, without OTC, Ammonia, Ornithine, and Carbamylphosphate should build up.
To your point about Ornithine being a part of the cycle and the cycle stopping, what you're incorrectly assuming is that OTC is necessary for Ornithine production. It is not necessary according to the figure. For example, Aspartate could come in and lead to the creation of Ornithine. The main point however, is that the Ornithine and Ammonia cannot be converted into their end product Citrulline and have no other pathway.
Although it could be said Ammonia becomes Orotic Acid? But there is no evidence that this reaction can overcome OTC deficiency in the passage so its most likely irrelevant to the question.
