There are multiple languages such as got and udm to give few examples that have once been exported but have since fallen below the export threshold.
It would be better to keep exporting these languages to follow of our mantra of not wasting translator's work by ignoring the fixes and additions they have made.
At some point though they might go so much out of date that T139941: Allow deletion of languages during export that are under a threshold might be a better solution.
Previously, when a language fell under the export threshold (% of translations completed), it would no longer get any updates from translatewiki.net. This lead to problems listed in T233581: Decide how to deal with languages that have fallen under export threshold. Now we keep updating such languages.