Ace and Luffy would escape.
Whitebeard would still be alive.
Luffy would reunite with his crew and have the thanks of Whitebeard and his crew for saving ace. They would go to the New World and would fail...that's the reality.
They wouldn't be strong enough to make it through. They'd probably meet their demise (although it pains me to say it) against Hody Jones on fish man island. They wouldn't even make it to Punk Hazard.
It was either Ace dies there to spur on the 2 years training or they blindly travel into the New World and meet their demise before they even start.
ruffy couldn'Tve lost to hody, because he'd traveled there 2 years earlier.
What would've happened is that The manga woulda taken helluva longer to develope because ruffy was so underpowered right then