。
As long as I live, I will never forget your kindness.
Literal
Life [subject-が] exist [limit-限り], your [possessive-の] honorable-kindness [object-を] forget-not.
~限り ('as long as, to the extent of') marks an extent or condition. 命がある限り = 'as long as there is life.' ご恩 is the honorific form of 恩 ('favor, kindness, debt of gratitude') — a culturally loaded term for obligations one incurs from another's generosity, central to traditional Japanese ethics.