Wings of Redemption
Animal Companions and Druid's Death
When a druid dies, their animal companion does not instantly revert to their basic animal form. Instead, the latent magics used to grant them their special powers fail slowly. Every day that the druid is dead, treat the animal companion as if they were bonded to a druid one level lower (cumulative), until the “effective druid level” reaches 0, at which point they revert to their basic animal form. If the druid is revived during this period, or within 1 week, the bond can be trivially reforged.
This theoretically also applies to rangers and their Animal Companions, but not Sorcerers or Wizards and Familiars (that magic fails fast)