This might go against all wisdom on this board but you know what, if this is tearing you up that much then I would say to go ahead and make the call.
One thing I don't ever want to do is go forward with a what if in my head.
I would speak to her cool, calm, and collected and tell her how you feel but not in a needy way or desperate if that is possible.
A few weeks before I started posting when W finally filed for the D I spoke to MC who gave me some good advice and I took it when I spoke to my W.
I told my W this "W. I would like to work things out if possible, but if you feel this is what you want then I want you to know that I am ok with it and I want you to be happy even if that means that you are not with me. I am sorry I've hurt you and I hope you find your happiness"
At this point I was ready to hang up the phone and go away. Well, that turned into a 2 hour convo with W and a good one too. That was the first time she began to take some ownership in the breakdown of the M. Of course I was willing to hang up the phone at that point. If you decide you want to give her a window asks to see her or give her a call and set her free. This way you have left her with a chance to come back.
I am sure I will get some 2x4 action for this advice but go with your instinct because part of my W problem was that I did not fight for my M or for her, I was too willing to let her walk away. That was my tough guy mentality. Every sitch is similar but they are all unique, only you know.
What is the worst that can happen? She goes through with the D? OK. You already knew it was coming..........