Hi Gooselady, I'm so sorry about the fox attack and the loss of your gander. It's devastating when that happens, as too many of us on here will know.
The first thing to do is to improve security if possible. Urban foxes have little fear of people and he will be back, or another will come. This is the time of year when adolescent cubs are leaving the litter and trying to find food for themselves, and in their inexperience they're even less cautious about what they attack. Obviously, make sure the remaining gander is safely in his house at night, but be aware that there may also be danger during the day. Do they just roam the open garden, or are they in a secure mesh pen?
I haven't kept geese, but yes, I think one on his own might well be lonely. It would be best to get a female if you get one at all, as two adult, unrelated males are possibly going to fight. You don't have to worry about having unwanted goslings as all you have to do is to remove any eggs laid in the Spring so she doesn't get a chance to incubate them.
However, how big is the garden? Geese are large birds that eat a lot of grass and they really need a large area where the grazing can be rotated. As you know, a lot comes out the other end as well, and they are quite noisy. Lovely as they are, not many people keep them in a suburban garden for these reasons. It sounds as if the garden belongs to your parents, and that they're not very keen on getting a replacement. One possibility, of course, is to rehome the one you have, and think what to do next about what poultry to keep, if at all.