When you say 'dragontree', I am thinking you mean Dracaena marginata.
When you say some type of animals were in the soil, I am thinking you mean insects or bugs.* When you say the "bole" is soft, I wonder if you mean the trunk, pole or base of the plant.* If parts of that plant I showed you a picture of are soft, then the plant has rot and will not live.* It sounds like the soil may have been too wet.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.