And if that file is gone... are the bitcoins unrecoverable?
If that file is gone, you have no backup of it, you can't use software (or hardware) to recover it from your disk, and you didn't export and save the private keys anywhere else, then in all likelihood the bitcoins are unrecoverable.
If you did delete it without a backup, stop using your computer right away so as to avoid increasing the chance you overwrite that portion of the disk that store the file. Then use the software mentioned above search for the wallet.dat file. You will want to install this software on a different disk and boot from that disk.
As above, is this Windows? Mac? If Mac, was Time Machine active? If Windows, see the poster above.