Well, the SRBs, once lit, will continue to burn until expended or sent a self-destruct command. At which point, they will continue to burn, at a significantly increased rate, until fuel is expended. Launch commit, with the Shuttle, comes with sending the ignition command to the SRBs, and you had better hope there is not a hang-fire or one of them fails to light.
That said, I've always wondered if you saw trouble coming several seconds away, if you couldn't flush the main engines with hydrogen (if there's oxygen in the lines during shutdown, SSMEs go kaBOOM!) and jettison the SRBs and the main tank as an assembly, then use the RCS jets to point the thermal tiles at the rocket plume.
It wasn't in the manual, but I'm sure someone at NASA discussed it over drinks after work at some point.