In a word, both Princip, and his conspirators, were unapologetic. They mourned more the death of Sophie as a regrettable accident that should have been avoided much more than the war that was consuming Europe wholesale. War, at least to Princip, was a necessary and unavoidable step to assuring a Yugoslav state free of Austrian interference. Princip saw the war as necessary, but also not really as a war. He thought he was sparking a revolt, a revolution.

To quote Paul Jackson in "' Union or Death!': Gavrilo Princip, Young Bosnia, and the Role of 'Sacred Time' in the Dynamics of Nationalist Terrorism":

We can glean further insight into Princip's thoughts on the assassination from a series of notes taken by one Dr. Pappenheim, a psychiatrist who conducted a series of prison interviews with Princip before he died of tuberculosis in 1918. In these interviews, Princip asserted his belief that his act would spark a wave of nationalist fervour - one that would be the prelude to an irresistible movement of national liberation. The role of the Bosnian intellectuals was, therefore, crucial.

In a word, Princip wanted war. he knew it would spark a what amounted to a war of independence for the Southern Slavs and the Balkans in general against Austria-Hungary. However, despite his awareness that war was possible:

[...]Interestingly, Princip showed he was aware of the contemporary instabilities in Europe that many intellectuals claimed portended a world war:

it is all indifferent to him, on account of his illness and the misfortune of his people. Has sacrificed his life for the people. Could not believe that such a World War could break out as a result of an act like this. They did indeed believe that a World War might break out, but not at that moment.

Pappenheim's notes go on to say that Princip was unable to feel contrition: 'cannot feel responsible for the catastrophe'; and that he felt that no good had come of the action: 'fears he did it in vain'.

To quote further from Jackson, this knowledge in Princip that a world war was possible, did not stop him. Indeed, if anything :

Princip's thought was clearly marked by a deeply held sense of utopian revolutionary nationalist, a varient of a palingenetic mindset:

[...]But we as nationalists, although we had read socialistic and anarchistic writings, did not occupy ourselves much with this question, thinking that each of us had another duty - a national duty.

And here, in these parts, it makes clear that while he had not gone out with the intention of starting a world war ("merely" a localized one, and more a revolt than a war), he was well aware of, and would welcome a world war if it helped further his goals of a Yugoslav state. As history would show, his fears of dying in vain were unfounded, for his dream of a unified homeland for the Southern Slavs was realized in the Treaty of Versailles.

That touches, briefly, on Princip, but there's also the matter of his other conspirators. The following is the interview between the president of the court, that is the presiding judge, and one of the conspirators, Vaso Čubrilović.

President: Did you want to fire at the late Archduke when the car came near?

Čubrilović: No.

President: Why? You were standing there with a weapon, intending to make an attempt on his life?

Čubrilović: Because I saw that she was with him. I saw the bomb falling and jumped aside so as not to be hit.

President: When did you give up on the idea of an attempt? On the spot, or sooner? Did you still have a strong resolve to carry it out?

Čubrilović: I gave it up on the spot. I was always strongly resolved to carry it out, but I did not know that she would be with him. I did d not expect to see her at his side.

President: But at the preliminary inquiry you said that you were sorry for him, too, when you saw him and that that was why you gave it up.

Čubrilović (leaning suddenly forward): Him! I was not sorry for him! (decidedly and defiantly). Not for him, but her!

President: You protest against the idea of having been sorry, as strongly as if I had insulted you by the suggestion!

Čubrilović: Yes. (Sensation in Court).

Now here is where it gets interesting. The President asks Čubrilović about his religious convictions, and at least in the case of Čubrilović, we know his view on this European butchery.

President: What do you believe? Are you an atheist?

Čubrilović: I certainly believe in God. I believe in everything.

President: If you had believed even a little, you would not have committed murder. I suppose you know that (our) faith forbids murder.

Čubrilović (suddenly): And who murders millions of men in European wars!

President: You are to blame for all that.

Čubrilović (aggressively): Not I, but people like the Heir Apparent. I may regret him as a man, but not as Austrian Heir Apparent. (*loud murmurs in Court).

Thus, we see that, at least in the case of Vaso Čubrilović the most obvious statement of indifference or even pride over what had happened. However, not all of the conspirators were so steely-hearted in their resolve.

Take, for example Cvjetko Popović, one of the other conspirators involved. We shall quote from the same transcript as before:

President (looks at him calmly for a minute): Were you a good pupil in school?

Popović: Yes, I was always a good pupil.

President: How then was it that you, who had always been a good pupil, plunged yourself into such a dreadful affair?

Popović (lowers his head and remains silent).

President: Are you even now sorry that it happened?

Popović: I am really sorry, for I did not know how dreadful the consequences would be.

Presumably it is at this point that I believe, given the pattern of earlier questioning, the President of the court is referring of course to the wider consequences: that is the war, the hardships upon Popović's Serbia, etc, etc, that came from the assassination. He then goes on, however, to individualize, as he had with Čubrilović.

President: And for the individuals, for those who fell in the conspiracy?

Popović: I am sorry for her.

President: And for him, are you sorry for him?

Popović (is silent for a moment, then says coldly): For him I am not sorry.

Once again, the conspirators are resolved in their desire to see the Heir Apparent, the Archduke of of Austria die, even as they show contrition for Sophie.

And Trifko Grabež holds similar views to those expressed by Čubrilović, though I don't know if the courts asked him, as they did with Čubrilović, or (presumably with Popović, given the pattern of questions on the other conspirators), about the view of the wider war and the longer-term consequences of his situation.

President:In the event of the Archduke having passed through Careva Čuprija, would you have shot at him?

Grabež: Certainly I should have. (He then tells how content (miran) he was after the news that the attempt had proved successful).

President: And did you know that the Duchess was also killed? Were you then quite contented?

Grabež: I should have preferred if Potiorek had been killed instead of her.

Now, I should make a note here as well that, for context of all of this, the trial was held in the Fall and Winter of 1914/15. Thus, the World War, while already at a scale beyond imagining of previous conflicts, had yet to reach the levels of suffering and butchery that your question seems to have supposed (not to belittle all that had already occurred of course, but the magnitude of things between August 1914 and the start of the trial in October 1914, simply put, pales in comparison to 1915, never mind '16, '17, or '18). Several of the conspirators, including Princip and Grabež, died in prison of tuberculosis before the war was out: Princip in April 1918, and Grabež in 1916. Of the men that I've excerpted, Vaso Čubrilović and Cvjetko Popović did survive the war. I'm not familiar if Čubrilović really spoke of the matter, but according to an article in the Saskatoon Star-Phoenix in July 1964, it is stated that Popović "says he would not have taken part in the plot had he dreamed it might lead to war".

Sources:

1. "'Union or Death!': Gavrilo Princip, Young Bosnia, and the Role of 'Sacred Time' in the Dynamics of Nationalist Terorrism". Paul Jackson. Totalitarian Movements and Political Religoins, Vol 7, No 1 (March 2006). Pages 45-65.

2. "The Sarajevo Murder Trial". R. W. S. W. The Slavonic Review, Vol 4, No 12 (March 1926). Pages 645-656.

3. "Errors in Assassination Led to First World War". Saskatoon Star-Phoenix. 4 July 1964.