Apologies for the long title, here's a JSFiddle.

Here are the steps to reproduce it, JSFiddle references in brackets:

• Create a component with a slot that has a v-else directive on it (MyWrapper).
• Create another component that imports/uses the first one (MyComponent).
• In the second component, create a custom directive with bind/unbind functions (myDirective).
• In the template of the second component, use the first component (wrapper) and insert an element with the custom directive inside it so it gets rendered in place of the slot.
• Call vm.$destroy() on your instance. This should call unbind on the custom directive, but it doesn't.

If you remove v-else from the slot in MyWrapper, everything works as expected. My current workaround is simply replacing

<div v-if="someExpression"></div>
<slot v-else></slot>

with

<div v-if="someExpression"></div>
<slot v-if="!someExpression"></slot>

Tested with latest (1.0.15) version.