He commended, however, the author’s way of ending his book with the promise of that interminable adventure, and many a time was he tempted to take up his pen and finish it properly as is there proposed, which no doubt he would have done, and made a successful piece of work of it too, had not greater and more absorbing thoughts prevented him.
This passage is extremely important to the text as a whole. It is basically hinting to the reader that part of the psychology behind Don Quixote's madness and warped perception of reality and events is that he is giving mundane things the passionate or intense ending he wishes they had, similar to the books he reads. Don Quixote finds it within his realm of ability to create alternate, superior realities and thus, shows the audience why he is so sure they are correct. The word "interminable" is used very calculated here, as it means endless and is "often used as hyperbole". This is extremely interesting in regards to the highlighted passage as a whole because it shows that Don Quixote sees his realities as endless and his adventures as ever lasting and that that idea as a whole could be viewed by sane people as hyperbole, but to him is not at all. Source: https://www.dictionary.com/browse/interminable