What happens if Hillary Clinton does somehow manage to become president? Eleanor Clift speaks for many when she says it'll be payback time:
Notables who abandoned her for Obama will get the Big Chill. "He's dead to us," a Clinton aide was quoted saying of John Kerry, who along with Ted Kennedy was turned off by the perception of race baiting that led up to the South Carolina primary. A major donor, conflicted between the two candidates and apologetic over his backing of Obama, found Hillary less than sympathetic. "Too bad for you, because I'm going to win," she snapped.
Maybe. On the other hand, current Obama endorsers include, among others, the Senators who chair the committees on Health, Education, Labor, and Pensions (Kennedy), Banking, Housing, and Urban Affairs (Dodd), Judiciary (Leahy), and Budget (Conrad). Unless Clinton is uncommonly stupid, she's not really going to try to govern the country while freezing those guys not. Nor would it make any sense to make a big push for health care reform while simultaneously freezing out the Obama-backers in SEIU.
Kerry is someone a President Clinton could plausibly afford to ignore, which is probably why he's used as the example, but it's actually pretty rare for a legislator to be noteworthy enough for his endorsement to matter and also sufficiently unimportant to ignore.