I just looked at the play again a looked through the rule book. (For those interested, Rule 2-12 (correctable errors), 2-13 (use of the monitor), and Rule 5 (scoring and timing) are all pertinent here. Rule 5-10 outlines when the clock is to be stopped, but every instance involves the official recognizing or granting a stoppage. The rule basically starts out by saying the clock "shall be stopped when an
official:" In this rule, there are no natural clock stoppages that occur within the game and only when the official stops it.
There are things in the correctable error and monitor rules that allow the clock to be reset, but only one that I see that specifically mentions resetting the clock to "the moment" something occurred. That is for an end game (clock reads zero before checking monitor) foul in which the rule specifically states that if a foul was called, the officials should reset the clock to when the foul occurred as opposed to when it was called.
The general rule for putting time back on the clock reads as follows:
"Determine the correct time to be placed back on the game clock
when the referee blows the whistle, signals for the game clock to
be stopped, and in his/her judgment time has elapsed before the
game clock stopped."
This rule applies to all situations including made baskets, timeouts, and fouls with any time left when the clock was stopped.
I just watched the Henson thing again on MMOD, and unfortunately all of the replays were during the studio show, so the only shot that is available is the live one. There are several problems in using this shot anyway. First is obviously that you can't get slow motion and the time between the ball hitting and the ref blowing the whistle/starting to signal is very very small. With the naked eye, I can't imagine that the ref was over half a second late, as .5 being left would indicate. The other issue with the live shot is that because of all the processing that the data has to go through, the TV clock (and the one on the ribbon lights and overhead scoreboard for that matter) is about 2-3 tenths late. Here is a photo of Hayward's last shot which conveniently illustrates this. As it is, it is really tough to tell without those replays that displayed the game clock what the proper time left would have been.
As for changing the rule, the committee for this meets every April after the season is over. The process can take varying amounts of time to complete for a rule depending on the importance, urgency, and impact. For example, rules adding or moving lines can take years to implement. They had initially talked about a charge circle before the 2010 season, but just got around to testing it during select in season tournaments this season, and a permanent line is likely still another year or two away. The rule allowing officials to go to the monitor for flagrant fouls and the enhanced penalty for elbows, however, were implemented immediately after they were brought up.