Forcing Surfer to close in the middle of a save usually corrupts the SRF file. Corrupted files usually cannot be recovered. This is best avoided, if possible.
You may want to consider clicking File | Options, checking Backup files before saving and clicking OK. Enabling that option will create a backup file (*.BAK) in case the original becomes corrupted in any way.
If the SRF file is missing after forcing Surfer to close in the middle of a save, one user reports success searching his hard drive for the file name with a TMP extension. Then rename the file with an SRF extension. Open it in Surfer and click File | Save As to resave it with a different name.
Updated January 24, 2017