ok so! I was looking at this photoset and the fact that it lagged a little made me realize something, especially while looking at this gif:
If you watched the scene, it mostly just sounds like Sebastian's making incoherent grunting noises. But looking at his mouth in this gif, he looks like he's actually saying something. The 'O' shape it makes made me think he was saying "go", presumably "let go" in this situation.
Then I went ahead and watched the cutscene again.
It's still really gross and garbled, but if you listen carefully, he says "Laura". He actually says "Laura, let go."
Sebastian would have died here. Even if it was unintentional, because she took her hands off his body, he was able to reach the panel. Laura let him go.