Recovering from a lost datafile in a UNDO Tablespace

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hi i want to knw whch conditions will lead to data loss:

scenario 1: database was cleanly shutdown and nxt time i find the undo datafile missing and i create new undo tablespace
                 will it cause data loss??

scenario 2: database crashed and i perform media recovery then will it cause a data loss??

scenario 3:  database up and running and i recreate new tablespace wil it cause data loss??

scenario 4: !-- @page { margin: 0.79in } P { margin-bottom: 0.08in } --> more then 1 file in tablespace and 1 gets corrupted
      and i recover that datafile database is up and runnin
      wil it cause data loss??

thanx in advance