I don't think HMV going under is good at all. The highstreet is dying in general as it is, and they still do some good deals in store. Not to mention the countless jobs that'll be lost from the retail, management and distribution sides.
Supposing though that another e-tailer doesn't bother getting any more steelbooks to replace them? If Play.com pick up the slack, they only post to Europe which might upset a few of our American friends. Sure, you can get them another way but (although they take forever to arrive), HMV is a lot simpler.