Destroy target creature. You gain 1 life for each artifact you control.
Bastien L. Deharme
The number of artifacts you control is counted only as Tidy Conclusion resolves, after the creature is destroyed. For example, if you destroy a Fairgrounds Warden that exiled your artifact creature, the artifact creature will return and then be counted when determining how many artifacts you control.
If the target creature becomes an illegal target before Tidy Conclusion resolves, the spell doesnâ€™t resolve. You donâ€™t gain any life.