If a redo log is missing, it should be restored from a Cold backup (if redo log backup available in Sunday Cold Backup) if possible. Here's an example, where I attempt to startup from SQLPlus when a redo log is missing:

SQL> startup

ORACLE instance started.
Total System Global Area 122755896 bytes
Fixed Size 453432 bytes
Variable Size 67108864 bytes
Database Buffers 54525952 bytes
Redo Buffers 667648 bytes
Database mounted.

ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1: 'C:\O\ORADATA\REDO01.LOG'

SQL>

To fix this we simply copy REDO01.LOG from Cold Backup.

SQL> alter database clear unarchived logfile group 1;

SQL> alter database open;
Database altered.

SQL>

That's it - the database is open for use.