Do you intend to throw away everything the clan has painstakingly built up, in an instant?
Literal
Clan [subject-が] struggled-and piled-up-[progressive-てきた] things [object-を], you [topic-は] one-instant [with-で] null-and-void do intention [question-か].
反故にする ('to make null and void, to throw away') — 反故 originally means waste paper (used manuscript paper), so 反故にする = 'to treat as waste paper.' 積み上げてきた ('has been building up') uses compound 積み上げる + ~てくる for accumulated effort over time. お前 is a rough, confrontational 'you.' The sentence drips with accusation.