Has the forest on your dacha land changed a lot over these years - clearcuts, new paths, construction nearby? Badgers are pretty sensitive to changes in their habitat, and even moderate disturbance can make them move to new territories. Plus, they dig burrows over many years, and if a sett is abandoned, it might just mean the family relocated, not that they died. The badger population in the Moscow region forests overall is holding steady, but local populations can definitely fluctuate depending on food availability, the presence of good burrowing sites, and the level of disturbance.