I say, with Allah's guidance: If a cat or something similar dies in the well, it is considered: If the entity in the well becomes bloated, all the water of the well must be drained. If it does not bloat, then 40 buckets must be drawn from the well as an obligation, up to 60 as a recommendation, after removing the entity from it. See: Al-Maraqi 37-38, Al-Bahr 1: 124, Al-Bada'i 1: 86, and Allah knows best.