Hi RachH72
This is a problem we have every year, with hogs disappearing. The worry always is that it is some sinister reason, but that isn’t always the case. There are loads of reasons why they might disappear. Females could be producing young ones, and males, who have bigger ranges, may be concentrating on other parts of their range – especially if the female is currently absent as well. There may be other females around in other parts of their ranges.
But there are other possibilities. Someone else nearby may have started providing food and water, the hogs’ route to your garden may have been blocked somewhere and the hogs haven’t yet found a way round, etc. With so many people with extra time on their hands, it may be that people have been doing repairs to their fences, etc. Some may even have been making hog holes as well, providing more options for the hogs.
I would keep putting out some food and definitely always leave water out, preferably all day every day, just in case. Hopefully some hogs will return and you never know, maybe even some hoglets later on.
Good luck.