So perhaps I’m missing something obvious in the rules, but when playing as a Animal Druid I have the option to grow my animal companion through feats. If I choose the mature animal companion Feat to make my companion a little better, and then it dies the next day, have I wasted a feat?
So for example, later on once I’ve potentially invested 3 feats in an animal companion, if it were then to die (or I were to dismiss it), would my Druid effectively be 3 feats lower than the rest of my party?
No. Two points.
1. Animal Companions should be using the same PC Dying Rules, so it shouldn't be regularly dying.
2. If your companion dies, you can spend a week of downtime to replace it at no cost. This new companion would benefit from your Feats the same as the one that died.
Is there some statement in the rules that prevents you from applying your animal companion feats to a new animal companion that replaces your old one?
I don't have the rules handy, but I am fairly sure that this issue would have come up if it were not possible to transfer such feats from a dead or dismissed animal companion to its replacement.