Can data on a dead hard drive be accessed?  I have to return it to the Mfg, and I want to know if I need to worry about it.
 It depends on how the drive died. Data on a "dead" hard drive can sometimes be accessed, by various methods, in ascending order of cost and time:

If the circuit board has failed one can swap it for one from an identical drive.

Specialist data RECOVERY companies have clean ROOMS where they can take a drive completely to bits and reassemble the platters with new heads, motor assembly, etc.

Outfits like the CIA have special electron microscopes which can take an image of a hard drive platter and reconstruct the data.

It all depends on how badly the data is wanted. These techniques range in time and cost from a few hours and maybe $500 to days and weeks and thousands of dollars, and even the cheapest and QUICKEST of them is very unlikely to be practiced by a hard drive manufacturer processing a return, as far as I can see. In any case, unless the data revealed evidence of serious criminal wrong doing, you would be protected by data privacy laws, I would have thought.

I read about a case of a cocaine smuggler in London who kept details of his transactions on a Psion palmtop, and thought that he had erased it all, but the police were able to read it all in their LAB and it sent him to jail for 14 years.

Then there was the notorious case of the pop star and child porn collector Gary Glitter, but that was a complete laptop with a functioning hard drive, he'd just messed up the configuration and sent it back to PC World and a curious staff member (against policy) had idly looked through the folders...

So if you are just worried about personal data such as bank and credit card details, I would not worry unduly, the hdd company probably has a policy in place to protect your data. You could enquire whether this is so. On the other hand, you feel reluctant to arouse their curiosity as to what might be on your drive. In this regard I would not worry unduly about pirated software or multimedia content or (legal) pornography. Such a discovery might provoke smiles at the hdd company but is unlikely to rebound on you.

Not that I am suggesting you have anything really bad, just giving EXAMPLES.