When a load is discontinued, any data already loaded remains in the tables, and the tables are left in a valid state. If the conventional path is used, then all indexes are left in a valid state.
If the direct path load method is used, then any indexes on the table are left in an unusable state. You can either rebuild or re-create the indexes before continuing, or after the load is restarted and completes.
Other indexes are valid if no other errors occurred. See "Indexes Left in an Unusable State" for other reasons why an index might be left in an unusable state.