slip out unobserved

Minutes later he watched her slip out unobserved by the group of men who were arguing as to who had the next dance with her.

Indeed he felt so choked in the stuffy little church that just before the sermon (which he happened to be aware was /not/ written by Beatrice) he took an opportunity to slip out unobserved.

I thought that I should be able to slip out unobserved in the morning with my clothes upon me, muffling my face with a white wrapper I had taken, purchase, with the money I had taken, spectacles and so forth, and so complete my disguise.