Imaoka Kiyoshi announced in his blog that his wife Kurimoto Kaoru passed away on May 26th. She was 56 years old and had been suffering from pancreatic cancer.

Sources:
Fuhou.com
GIGAZINE

Update
According to Yomiuri Online, Kurimoto Kaoru had already written Guin Saga up to the volume 129 and volume 130 halfway. She gave up writing the novel on April 23rd and was hospitalized on May 7th. Hayakawa Shobo will publish the incomplete volume 130 as well as the remaining volumes 127 - 129.

Guin Saga was applied to Guinness World Records for the longest novel record in 2004, but was rejected because Guinness judges considered that it's not a single book.

Source: Yomiuri