Is there a word for returning to unpreparedness? [closed]

There is the phrase "stand down" about which Lexico says

stand down
PHRASAL VERB

2 Relax or cause to relax after a state of readiness.

If something doesn't happen soon, I reckon they'll stand us down.

An ambulance crew was dispatched immediately, however they were stood down shortly after.

They have got to accept that the war is over and stand down their army once and for all.

I'm trying to describe a situation in which a person prepares for an event, then realises the event won't happen, and so they undo their preparations, returning to a state of unpreparedness.

You're literally just describing

relax

...to loosen...
...to diminish the... tension of...
...to make less tense...
...to cease or lessen one's efforts...
...to allow... to slacken or diminish...
...to slacken or become less severe with regard to something...

As far as actively going about undoing one's preparations, it would depend on the situation: striking camp; unloading, dropping, reholstering guns; replacing food; turning off the car, &c. For people like the military and police with prearranged readiness levels, they just talk about the levels themselves: returning to [former level] or ending, recalling, ceasing, &c. [emergency level].

This seems like a pretty exact fit, though I'm not sure how frequently it is used:

Unprepare

: to cause to be unprepared : make unfit or unready

_{Source: Merriam-Webster, https://www.merriam-webster.com/dictionary/unprepare}