Ar-Rum: (8) "Have they not reflected..."
{In their own selves}
It may be an adverbial phrase, as if it were said: "Have they not initiated reflection within their own selves?"—meaning, within their hearts, which are otherwise void of thought. Reflection occurs only in the heart, but this is an added depiction of the state of those who reflect, similar to saying: "Believe it in your heart" or "Conceal it in your soul."
Alternatively, it may be connected to the verb "reflect," as in saying: "He reflected upon the matter" and "He turned his thought over within it."
{What Allah created}
This is connected to an implied verb, meaning: "Have they not reflected and thus said this statement?" It is also said that it means: "Have they not reflected and thus known?"—because the context provides evidence for this.
{...except with truth and for a specified term}
Meaning: He did not create them in vain or as a trifle, without a valid purpose or profound wisdom, nor did He create them to remain eternal. Rather, He created them accompanied by truth and wisdom, and with a predetermined term to which they must inevitably reach—which is the establishment of the Hour, the time of reckoning, reward, and punishment. Do you not see the words of the Exalted: "Did you think that We created you in play (without any purpose), and that you would not be brought back to Us?" (Al-Mu'minun: 115)? See how He labeled the notion of them not returning to Him as "play" (vanity).
The ba (preposition) in {except with truth} is like your saying: "I entered upon him with (in) my travel clothes," or "He bought the horse with its saddle and bridle." You mean he bought it while it was accompanied by the saddle and bridle, inseparable from them. Likewise, the meaning is: He did not create them except while they were accompanied by truth and bound to it.
If you ask: If you make {in their own selves} connected to "reflect," what is the meaning?
I say: The meaning is: Have they not reflected upon their own selves, which are closer to them than any other creation? They are more knowledgeable and informed about their own states than they are about anything else. If they were to contemplate what Allah has deposited within them—outwardly and inwardly—of the wonders of wisdom that point to deliberate design rather than neglect, they would realize that they must inevitably reach a time when the One who designed their affairs will recompense them: rewarding the good with good, and the evil with its like. By doing so, they would know that all other creatures are likewise governed by wisdom and design, and that they too must inevitably reach that appointed time. The "meeting of their Lord" refers to this "specified term."
Ar-Rum: (9) "Have they not traveled through the land and observed how was the end of those before them? They were greater than them in power, and they plowed the earth and built it up more than they have built it up, and their messengers came to them with clear evidences. And Allah would not ever wrong them, but they were wronging themselves."