It might be a good idea to get it checked out to make sure it isn’t a new infection, injury, etc. But, and others may disagree, but if the hog is behaving normally otherwise and knows it’s way around I would allow it to remain in the environment it knows. Alternatives would be some sort of captivity – even a walled garden is just bigger cage – and the hog would not be familiar with those surroundings.
Hogs have pretty poor eyesight anyway and of course are normally around at night. They rely heavily on their sense of smell and hearing. I think it is likely the hog would have been aware of the slugs but chosen not to eat them. The slugs which hogs might eat are usually the small to medium ones and very often those that congregate around feeding areas are the larger slugs that most hogs will ignore. Slugs are not especially most favourite food for most hogs.
Re. water and hogs. Their view seems to be ‘why walk round a water bowl, when you can just walk through it’. So that is quite normal behaviour for any hog.
I write with some experience of a hog showing no eyeshine (at all). This particular hog was one of the hoglets from 2018. She chose not to hibernate the winter of 2018 – 2019. She continued to grow all through the hibernation period. Very unfortunately in the Spring of last year she somehow managed to get a life threatening strimmer injury, from I know not where. (That can happen to any hog and their state of vision would not be relevant). Despite being so badly injured, she made her way back to my feeding area. She then went to the local Wildlife Hospital where she spent months being treated by the amazing people there.
There was a discussion as to whether she should be released into a walled garden, but I argued that her best chance of being a ‘normal’ wild and free hedgehog was to return to the area that she was familiar with. I took advice from someone else knowledgeable about hogs, who agreed and the Wildlife Hospital also agreed that she could come home. Of course, there was a certain amount of trepidation on my part releasing her again. Would she remember it all after such a long time away, and the trauma she had been through, etc.
She eventually came home and was released back near the feeding area which she was familiar with. She was placed in a hog box which was opened at dusk so that she was able to exit as she chose. She came out had a good sniff around, explored the immediate area and returned to the area (but not back into the box) then eventually disappeared into the dark. I left the box as it was, but she didn’t return to it.
To cut a long story short, it was not long before she was returning every night for food and drink at a fairly regular time, as she had done before her injury. She was also regularly seen foraging for natural food. She returned a bit smaller than her contemporary former hoglet, but soon made that up. After several more months of freedom (by then Winter) she disappeared – hopefully to hibernate. In the meantime she had been a wild and free hog for many months.
Of course, I hope that she will eventually return from hibernation, but as with all hogs, there is no guarantee of that. I know there are already some hogs back, but the males tend to return before the females and I would not be expecting her to return yet.
Occasionally, if I moved something, she might have looked as if she was bumping into it. But that occasionally happens with other hogs if something is suddenly blocking a route which was previously open. I tend to keep things in the feeding area pretty much as it always is, although I did have to create some obstructions because of a cat and the hog still found her way to the food. The hogs in my garden always seem to use the path to enter and exit (which always makes me laugh) and video showed that she trotted up and down the path pretty much like any other hog.
So basically, a hog is always likely to do best in the area which it knows. If the hog is coping well my feeling is that it should have a chance to continue to be wild and free. The only proviso, as mentioned at the beginning, is that you might want to get the hog checked over to make sure it isn’t a new injury/infection, which could potentially be treated. But if it needs treatment, I would argue for the hog to eventually return to it’s home.
I hope that helps.
Good luck to you and the hog.