Hi ,
Try to do incomplete recovery by using backup control file or hot backup before you drop datafile.

Then you can open the database with resetlog.

Well I think this must work.
You will loose some data , which u have added after droping the datafile. Otherwise this must work.


Then take immediate complete backup of ur database.

But this will work with database in archivelog mode only.

Or You can try tablespace point in time recovery also.