For a number of reasons, I think we can conclude that it would have been different had Dumbledore's death not been impending:
- Dumbledore had other ways of protecting Malfoy:
Remember that on the top of the Astronomy Tower Dumbledore tells Malfoy that he and the Order can protect him...that he should join the side he truly belongs to. That seems to be an authentic offer, as Dumbledore [accurately] believes that he can protect almost anyone from Lord Voldemort. So, if he weren't dying, he probably would have approached Malfoy with this offer earlier when his back wasn't quite literally against the wall. Of course, at that moment, he wanted Malfoy to get out of the way so Snape could fulfill his plan with the Elder Wand...
- All of Dumbledore's measures in HBP are put into effect rapidly and seem out of character:
For this question, a really important scene is when Dumbledore and Harry are in the Burrow shed, and Dumbledore begins to tell Harry about changes for this school year. Harry is surprised to hear that Dumbledore endorses him telling Hermione and Ron the contents of the prophecy (Dumbledore knows they will be vital on his journey) and shocked to hear he will be having private lessons with Dumbledore. Now, these private lessons might be the result of Dumbledore realizing his "Flaw in the Plan" from OOTP, but even in that discussion in his office, he isn't perfectly candid with Harry about what he has to do. Why not just explain about the horcrux(es) at the end of 5? Because he didn't plan on doing it so quickly. When he poisons himself, he realizes he must put everything into action and FAST. Importantly, he anticipates after that discussion in 5 that he has several years to expound upon Harry what he needs to know.
- Dumbledore makes a pivotal quote which--although it seems simple--answers this question:
“Well, really, this makes matters much more
straightforward” (DH, The Prince's Tale, Hardcover).
This quote implies that things were previously not straightforward, and he needed to deduce a plan by which he could train Harry over time and still have Snape "kill" him.
In other words, "I had another long-term plan about when you will need to kill me for the sake of the Elder Wand, Snape, but now we can just do it now and protect Malfoy, too."
A final thought: I do not think JKR would have had Dumbledore curse himself in the manner he did if the events of HBP would have happened anyway. She could have had Dumbledore simply die of old age in HBP, but know he was dying and thus need to train Harry and have Snape kill him. By having Dumbledore put on the cursed ring, JKR is attempting to show the dangers of the Hallows, that Dumbledore did in fact have a tragic flaw, and that his tragic flaw almost jeopardized his whole 16-years-in-the-making grand plan.