I am glad you wrote. I am so sorry to hear of the loss of your 10 year old daughter. And now this-- I am sure it brings it all back. Having someone leave you unexpectedly is devastating, and your feelings are well justified.
Nobody will be able to give you a percentage of his chance of coming home... maybe not even him. You said he didn't tell you his feelings, but did he give you a reason for his leaving?
The majority of marriages do not survive the loss of a child. Have the two of you been in a grief support group together? Counseling?
What sorts of things has he said in the past that indicate he may not be happy? Sometimes men deal with grief in a way that gets them past it -- is he saying that you are not moving on?
People deal with grief differently, and many women take many more years to get okay... if there is such a thing after the loss of a child.
Have you been to a support group, specifically for the loss of a child?
Have you emailed him, or mailed a letter saying this to him?
Just a quick follow up note... how are things?