Yes, your understanding about 伺う is correct. That's exactly why 伺う can't mean "to ask" there. Now I wonder why you couldn't reach the correct translation "to hear" when you initially read that sentence...
Well, somewhen I read in my textbook, I think it was when the dictionary form was introduced, that in colloquial contexts か can be left out in questions^^ That was one aspect which contributed to my confusion. The other was that I struggled a lot with 社長は, because I didn't know that this is a common way to address someone in second person. From such "blocks" in the understanding of a sentence, often further problems arise...^^
You seem to be overly bothered by the English term "adjective".
I wouldn't call it like that, but yes, I do have some issues dealing with the way japanese forms and uses its verbs as "adjectives", or better, "attributes".
What I was asking above was centered around two aspects of lingual category:
word class and syntactical function.
What I wanted to know here was into which word class 払わなければならない has to be put. Is it still classified as a verb, or is it a (deverbal) adjective?
However, from what you've written now, I can assume that the word class of adjectives doesn't really exist in japanese, right? Words like "yellow" in english are pure adjectives for example, they don't stem from any kind of verbal or nominal origin (at least not from a synchronous perspective, under a historical perspective there probably would be another word class it originated from).
This kind of "real" adjectives doesn't exist in japanese, it's either nominal or verbal morphemes which are coaxed into functioning as attributes, right?
So, since I would also like to be able to make it through sentences like the one in question without having to ask the same thing over and over again in the future,
can I assume then that, even if a ない-form of any verb behaves like an "adjective" morphologically (the switch from い in ない to く in なく is something I would associate with i-adjectives, although only in context of an adjective -> adverb conversion so far), there is nothing special at play and I can just proceed?
To make this clear, I'm still not sure wether the way I handle this is correct or not. Therefore, I will probably bring up such constructions again and ask wether I interpreted them correctly.
But I think I got the theory behind it, so I don't need to wonder that much when I encounter a verb functioning like an "adjective" in a predicative manner like here ^^