The lifetimes of high-energy lattice vibrational states of a-Si:H are calculated on the basis of vibrational localization for energies omega > omega(c), where omega(c) signifies the mobility edge. Anharmonicity-induced localized vibrational state hopping, with the emission of an extended vibrational state (a phonon) is found to be the dominant decay mechanism. Because of the contribution of the same vertex to thermal transport via localized vibrational state hopping, the vibrational lifetimes can be expressed in terms of this hopping contribution to the thermal conductivity, with only omega(c) as an undetermined variable. At low temperatures, the high-energy vibrational lifetime is found to be proportional to (omega(c)/omega)(4) exp[(omega/omega(c))(d phi/D)], where d(phi) is the "superlocalization" exponent appropriate to random vibrational networks at the hopping length scale, and D is the fractal dimension. Taking omega(c) = 40 cm(-1) for a-Si:H from the plateau temperature, and the ratio d(phi)/D approximate to 1.22 from estimates for percolating networks in d = 2 (there are no comparable calculations at the hopping length scale in d = 3), we find vibrational lifetimes of 1.1 ns (TO, 480 cm(-1)), 0.8 ps (LA, 300 cm(-1)), and 17 fs (TA, 150 cm(-1)). These values ate not inconsistent with recent observations of Scholten et al.