you don't know that, no one knows that,
I think the fact that she would have died in the explosion would have hurt Bruce a lot much more than being betrayed, think about it, the first woman he likes and cares about in 8 years, the first woman to care about him,
and she dies in an explosion, like Rachel, add the destruction of Gotham,
by that time he would probably not want to live anymore, he would have been completely destroyed, much more than Talia making a super cheesy video announcement:
"Guess What Bruce? I slept with you to gain your trust but I am really the villain and now Ima Gonna Die!"
Brilliant
. 
