I'll start off by apologizing if the answer to this is lurking somewhere on these boards, but I've spent a bit of time trying to find that answer to no avail.
According to my understanding if I cast the 5th level druid spell on my animal companion, it gains the listed benefits from the spell, 2d6 int, 1d3 cha, 2 1d8 HD, and then ceases to be an animal companion, removing all the benefits it had gained from being that companion and reverting to its base creature.
Now to what I'm unclear on. How complete is this reversion? Do I simply look up the bestiary entry for the creature and apply the bonuses from Awaken? What happens when the bestiary entry contains a creature with significantly higher HD than it had prior to the spell's casting? Does my late companion grow in size to match the normal entry like in the case of a T-Rex or Roc? If I follow the advice listed in the spell entry and take on my old companion as a cohort what sort of CR adjustment (if any) is caused by the spell's effects?
I could go on with the individual questions here, though I suspect any solid answer to one would actually cover quite a few of the others.
Thanks in advance for any answers.