What is a word that means "the outcome resulting from a lack of action"?

Solution 1:

Default Option

The default option is what the system -- or life -- does to you, or for you, when you choose not to take an action.

Wikipedia, the Default Effect (Psychology) https://en.wikipedia.org/wiki/Default_effect_(psychology)

Amongst the set of options that agents choose from, the default option is the option the chooser will obtain if she does nothing.

For example, if you have to check a box on a form for your employer to withhold money for an IRA, and you don't check the box, the default option goes into effect, and you don't have a deferred tax savings plan.