@Fire Fist:
I've considered this, but the fact remains that Shanks spent 2-3 years of his life with these two boys, and Ace was always stronger than Luffy growing up. Shanks sees potential in both Ace and Luffy, but Ace is (or was, rather, assuming he's dead) stronger than Luffy, and has already entered the New World, has established himself as WB's 2nd commander, and accomplished almost everything Luffy has set himself out to do.
Luffy hasn't seen Ace in 3 years, and therefore despite their brotherly bond, Luffy is a simple-minded person who would not see Ace's demise as a hindrance to his goal. Like any sibling, Luffy will certainly be angry or dismayed, but Luffy's apparent detachment from his past obviously indicates Ace's demise would not affect him as much as it would a normal person. Look at the callousness he expresses towards his grandfather, and the disassociation with people they meet along the way. Not once has Luffy said, "I wonder how Makino is doing," or, "I wonder how Vivi is doing," or anything else of that nature. Luffy's lack of interest in the going-ons of the world makes it clearly apparent that Shanks did not try and stop Ace for Luffy's sake, but either for Ace's own, or the love that Shanks has for Ace, either as a father (If they indeed are father-son), or a big brother (if they are not father-son).
so what your basically saying that if your focused enough on your goal it doesn't who dies around you? i think the answer to how Luffy would react to Ace's death is quite obvious based past reactions. Luffy goes into a rage when u mistreat or hurt his "nakama" who he's known for 3 - 4 years. so his reaction to the death of his "brother" ,who he grew up with, he would go into a blind rage and set the sea a flame searching for BB.