The above two problems still eluding me. I have, however, now also found the marriage of Sophia Gilbert, who was married 6 Feb 1848, in the same church as her sister. Her father James is shown as deceased. So he was alive in Dec 1843, but dead in Feb 1848. The suggested death date of 1845 is looking better and better.
Update: however at the marriage of Sarah Gilbert in Sep 1847, again in the same church, he is NOT shown as deceased!