No (unless it was changed very lately).

NOLOGGING option means only that during index *creation* redo information is not written to redo logs. This means much quicker creation of the index, but once the index is all changes to the index (caused by inserts, updates or deletes) are recorded in redo logs as usually.

So only if your database crashes after you create index with NOLOGGING and before you've performed a backup you'll have to recreate that index. After you've performed a backup you are safe regarding that index (unless you perform some other nologged action, like direct load, in the future).