Siataga returned to teaching for two terms this year, but saw a doctor after feeling unwell.
Within about three weeks he declined, was transferred to the emergency ward and died.
He had other health conditions which complicated his recovery, his niece said.
Siataga, 61, was renowned for being a caring educator, a lover of music and a big supporter of Polyfest.
Throughout his career, he worked at many schools including Forbury School, Kaitangata Primary School and Carisbrook School.
He also spent nine years as a teacher and a principal in Papua New Guinea.
Moonlight Macraes School board of trustees presiding member Georgie McGregor said the school planned to honour him with a memorial garden near the front of the school.
It was an area that Siataga always wanted to make use of, she said.
As a principal, he was ''completely devoted to the children''.
Siataga had a deep passion for music and grew up involved in the Dunedin Sound scene.
He shared that love with the pupils and taught them a variety of fun and unique songs.
Pupils never misbehaved around him, but he was never strict, she said.
Zen Teasdale was taught by Siataga at Forbury School more than 10 years ago, but he stood out in her mind as the most generous and caring teacher she ever had.
"When you spoke to him you knew he listened and cared," she said.
She remembered he would buy Christmas presents for pupils who had a rough home life so they had something to enjoy over the holidays.
"He was meant to be a teacher. That was his calling."
A friend and fellow educator, Pip Laufiso, said Siataga would always go out of his way to ensure pupils felt included and had opportunities - whether that meant dropping them off to sports practice or finding equipment for them.
Siataga "really demonstrated what it meant to care for children", she said.
He was one of Otago's longest-serving Samoan educators and one of the few Pacific principals.
McGregor said Moonlight Macraes School had an acting principal in place but was advertising for a new principal.
Siataga's funeral was held last week.