Sorry to hear that all the hogs there have disappeared. Several people have said something similar, but it must be very sad for you.
There are lots of possible reasons why they might stop visiting, such as, someone else is feeding them, their route there has been blocked for some reason, a badger has moved into the area, etc. and you may never know the real reason.
It is impossible to know whether or not they will re-appear next year, but as it is getting near to most of the hogs hibernating, they may not be back this year. Fingers crossed that some of them return at some stage and sorry I can’t be of more help.