Recovery Manager Restore and Recovery Techniques - Oracle 10g/11g Data and Database Management Utilities - page 134

In the image the RESTORE procedure is shown, it is not a requirement to open the
database. You only have to put the missing datafiles offline. The missing datafiles
can be restored and recovered after the database is open.
The last step in this recovery process is to put back online the recovered datafiles:
SQL> ALTER DATABASE DATAFILE 4 ONLINE;
SQL> ALTER DATABASE DATAFILE 5 ONLINE;
In the next image the datafiles are set online and the status is verified from the
V$DATAFILE_HEADER dynamic view. There it can be seen that there are no more
datafiles listed in the V$RECOVER_FILE view, this means all missing datafiles have
been recovered and there are no further recover actions to be performed.