Your situation is exactly why backup and recovery should be one of the DBA's top priorities. You can always reload and reconfigue software, but in many cases, it is difficult, if not impossible, to recreate data. I don't think you have any way to recover this file. You can contact Oracle Support, and they can use a utility to recover the data in the datafile, but from what I've heard, they charge a lot of money for this type of work.
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