James Maddrell was a farmer and judging from the inventory of Margaret Maddrell nee Callow (not on Brian Lawson's site) was doing reasonably well. Land records need to be checked. The HMS Captain (of which James Maddrell was a member of the crew) had returned to Southhampton by the time of your suggested remarriage, so he coould have returned to the Island.
Margaret Maddrell's administration was particularly informative on the Callow side since it located several of her siblings who I otherwise wouldn't have been able to trace with any certainity.
Margaret Callow Maddrell was a member of the Croit Roie Callows of Lonan who were written up in the 1992 IOMFHS Journals. A revised copy is in the MNH library.