I’m sorry to hear they put the hog to sleep.
Advice from the BHPS/Vale now suggest hogs can survive well without a hind leg as long as no stump is left. However, this isn’t everyone’s opinion as obviously they are unable to remove parasites on that side.
You are correct that most hogs come out of hibernation underweight and this one may well have been okay with some help.
However all health professionals have to make their own call on these issues.
As to colouration, yes they have different colours and markings. Nic is likely to give you very good advice on how to identify hogs.
As they get older they often become more ginger in colour
Hogs don’t have territories as such. I suggest you continue to put food out. There are obviously hogs in your area and it won’t take long before they turn up
Good luck
