slip away
steal away
sneak away
sneak off
sneak out

Where was she sneaking off to in the dead of night, especially after all he'd done for her?

She sneaked off with me last night and I put her up alone in a room.

She had half a mind just to sneak off and hide.

What's his idea of sneaking off to eat by himself?

Where did you sneak off to, right when there's work to be done!

And if so, why did he sneak off by the six train in the morning without a word to anyone?

But why did he have to sneak off like that?

He tried to sneak off again, this time earlier to avoid the little man, and through a window.

Why don't you sneak off for a couple of days' rest?

And I am certain we could not sneak off anyway.