No, it is most likely that Jim Macpherson did not come back from the war.
In the sellotaped notepaper it was written that the letter was Jim’s last letter. Connie Macpherson did not receive any more letters from him. It indicates Jim Macpherson’s demise. The incident took place around the earlier part of the World war I in which the Germans had been victorious which implies the defeat of the British and the demise of Jim Macpherson.