The bus (or A bus) will wait for stragglers. But you may find you aren’t well received by those stuck waiting on your bus if you take extra long.
However, you’ll have a much harder time trying to eat late and hang onboard that late. By 9am CMs are clearly urging people towards debarkation and by 9:30 they want you off-now. late breakfast in the MDR is 8:15, Cabanas stops serving by 8:30, pretty much nothing else is open. Remember how eager everyone is to get onboard to start a cruise? Another whole set of people is waiting to board the day you debark.
Enjoy your cruise!