Yes, the DOT rules area still I effect.. And as noted, many of the rules are now also contractually specified items as well..
However..... As it is with many aspects of air travel, they are not always 100% "clear cut" in terms of what does or does meet the standards and there are some subjective and noteable exceptions.
As example only, the DOT rules do not explicitly state what does and does not meet the standards for provisioning of food and/drink onboard.. Therefore, unless or until the DOT issues more definitive rulings on this, it can be debated what exactly meets this standard.. Carriers tend to provision items that have either low cost and/or are low "carry" costs..
For the "drink" side, that tends to be water or whatever beverages are provisioned as a standard matter... On the "food" side, they tend to focus on items that are shelf-stable and have longer "hold" times.. Granola bars, chips, nuts, or the like tends to be common items.
As for the deplaning.. There is one large caveat.. As is the case with most all apse at of aircraft movement, the final decision as to the question of "is it safe to do so?" is delegated, by law, to the Captain or acting Pilot In Command (PIC).
The DOT rules do not and cannot override or usurp the discretion of the Captain or PIC in this aspect.. If s/he feels it is unsafe to do so, then that specific aspect of the rules are waived.. But that's only for that one part...
The issue of what happens if you deplane..... What about reboarding?
This is a part of the rules that (IMHO) should have been better thought out or guidance given.. The DOT rules do *not* require a carrier to wait for, to take or to make any specific actions to identify and reboarding passengers who in invoke their DOT rights to deplane..
Therefore, until or unless there is either a percent setting judicial ruling (that remains after any appeals) or the DOT gives more guidance, the carrier does not need to wait or to take any specific steps to find, wait for or otherwise get everyone back onboard.
While common sense and logistical issues says you do what you need to do to get everyone back onboard, IF you can't or can't do so timely (ie you finally have a takeoff slot assigned or the crew will "timeout" so leaving promptly is critical) the carriers are presently free to go with or without you and if you're left behind the denied boarding rules would not apply (you boarded initially and the flight number did not change) and the carrier would have no obligation, other than traditional rebooking processes, to you at that point.
The DOT rules in this respect are rather new, and aside from a handful or so of cases of violations of the holding time, we've not yet seen any large scale test of some of these issues - like exactly what does or does not meet the food and drink rules? And what happens if you deplane and don't reboarding?
To be fair to the DOt, I don't think its possible or advisable to write law into the smallest minutia, but.... I also think that better or more encompassing guidance might have been helpful so all parties invokved have an Idea of what is or is not the "intent" of the relevant statue; and therefore what might or might not be an acceptable solution when all relevant variables are taken into account.
Edited: 9:45 am, June 14, 2013