Let's say it was subject to +100V at the output. That means that about 1 amp of current would flow through R518 + R519, Q507 and R515. That means 0.5A through each of R518 and R519, which means 50V across them and 25W dissipation, 50X their rating. They are small metal-film resistors and very well might blow quickly and quietly. R515 is a 47R 2W carbon composite, that seems much less likely to blow quickly. Q507 has a rated collector current of 0.6A, so a brief 1A pulse likely won't kill it. Also, if Q506 or Q507 were blown, whether short or open, I don't think I'd expect "no output" but either noisy, clipped output or large DC offset. So, I'm thinking R518 and R519 are blown and that's the first thing to check.