Valmiki Ramayana Sundara Kanda Sarga 55 Shloka 17
Original Shlokaविनष्टायां तु सीतायां तावुभौ विनशिष्यतः। तयोर्विनाशे सुग्रीवः सबन्धुर्विनशिष्यति।।5.55.17।।
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सीतायाम् When Sita, विनष्टायाम् is lost, तौ उभौ those two, विनशिष्यतः will die, तयोः of those two, विनाशे when they are dead, सबन्धुः including all relatives, सुग्रीवः Sugriva, विनशिष्यति will perish.
'If the two princes know about Sita's loss they will die and when they are dead Sugriva would perish along with all his relatives.