Broadcast in HD on BS11, but it's an upscaled.
Also, here's DVD sales of Vol. 1 from both seasons:
*74 19 **1,258 **7,912 **2 さよなら絶望先生 第一集 特装版
Second week and first week total is 7,912 for first Vol. of first season.
*34 -- **5,251 **5,251 *1 俗・さよなら絶望先生 第一集
First week total of second season is 5,251 which is pretty low, compared to the first. (But still a "success").
Starchild is always hungry for money, so third season is unlikely.