I don't know, I read the email and it didn't really sound "so final" to me. I know the sitch you are in sucks right now, but if you aren't ready to give up, then don't. Continue the DB'ing. If you haven't filed and she hasn't filed, just hang in there. Like I said, it sucks, the whole process sucks, but if you aren't ready to let go, then there may be hope. You won't ever know unless you try. I thought there was no hope in my sitch quite a few times and that H was just done and we were through because that's what he said, but I never gave up and we are ok now, truly better than if none of this had happened.
Figure out what YOU want to do. I don't think anyone can tell you when it's time to give up -- that's going to be strictly your decision. When you are ready to bow out gracefully. There are some people on these forums who have been at it for YEARS. If you don't WANT a divorce, then don't file and don't push her to file. I had plenty of people thinking I was insane for staying and putting up w/ what I did. But that is YOUR decision and your choice to make.
Me: 38 H: 35 S4, S5, S10 Bomb 01/07 Wanted D - nothing would change his mind Numerous A's prior to D bomb; EA prior/during D bomb Piecing 04/07 Deployed for a year 05/07 Still Piecing 2010 M 11 yrs 05/10