To stop the a/c you have partial spoilers and acc. brake pressure (7 application ,no reverse ) .
Now you have to think ,as usual , from where you are taking off . It is a 4 km rwy dry ? No problem , but what if you are departing from short wet ,contaminated rwy ? You will be able to stop ? So knowing that you lost both AC bus , ok scaring everything go black , you need to rotate on stanby instruments but after second with the RAT the screen will be back on , get airborne you can reach an holding ,make an assestment , decide if go back to the same rwy or looking for a longer one , perform the approach full briefed on what you miss from sys ,brake, rev. etc. . It is not safer than rejecting without knowing if you will be able to stop before the rwy end ?