well a reboot, doesnt neccessarly mean the end of our well known and loved characters, but more of an end of the "survival action" setting that 4 and 5 both had.
its my understanding from reading the interview on 6 that they intend to re-work the playing system to keep Resident Evil fresh-faced and rejuvinated while keeping the core characters intact.
Resident evil without Jill, Chris, Claire or Leon would be like Street fighter without Ryu and Ken, it would kill the series quicker than putting in a terrible plot.
Change is always neccessary to keep things moving along, but too much change would see Resident evil become another game under the same title and unappealing to most fans.
So in closing, they need to include the main story characters in RE6, or I reckon it might well lose them a lot of fans...