The pity is that the Twitter account is owned by Dennys Hsieh, a Taiwanese resident.
Scanning his Twitter page, it seems that Dennys was a very early adopter of Twitter - there are posts as early as March 2007 although he seemed to become dormant around the end of 2008 with only sporadic posts since that time.
Denny's does indeed own two Twitter accounts: DennysAllNightr and DennysGrandSlam - both of which promote various aspects of Denny's product offering. They certainly don't own the only account name which is promoted.
Alan Miller, co-owner of Filter Creative Group (Denny's social media management company) said that the menu mistake was a "simple misprint." Judging by this author's experience with the approval process for such items, that seems a rather disingenuous comment. It seems more like "wishing will make it so."
The erroneous menu has been in stores since October.
Denny's claim to be in contact with Twitter to re-assign the name to the Denny's restaurant chain on the basis that the domain has been idle for at least 6 months (that is true, but there have been posts to the account in the past couple of days).
The issue is that whereas "cyber-squatting" is easily overcome, Dennys Hsieh has a clear and unambiguous claim to the name, making any such hand-over demand difficult to achieve.
No matter what the outcome, Denny's has egg on their faces (and bacon as well!).