Board Thread:Questions and Answers/@comment-31.220.208.150-20150705010846/@comment-26281299-20150705041541

Pike was killed by a lucky critical hit in the battle with the first major "big bad" the group had to face, a Glabrezu (D&D 5E Monster Manual p. 58). This was before the broadcasted episodes. To save her, the group brought her to the healers of Emon, and the entire group had to go through several rounds of rolling dice against quite high DCs.

You can hear about it on the links below:

First Q&A and second Q&A.