In the scenario I provided you have heard V1. At or before the point at which you heard V1, you initiated braking and retarded the thrust levers.
2 seconds after you initiated braking and retarded the thrust levers you realise the brakes are not working. You are now over V1 and the engines are spooling down.
Do you:
(1) un-make your decision to reject, advance the thrust levers and attempt to take off, or
(2) look ahead and crash visually.
Those seem to me to be the only options. The availability of (1) would seem to me (as a non-expert) to depend mostly on how much the good engine/s would have spooled down in the seconds between retarding the thrust levers and the realisation that the brakes have failed (2 or 3 seconds), and how long it would take the good engine/s to deliver sufficient take off thrust after advancing the thrust levers a second later.
Somebody in PPRuNeland must have experience in how much a 'modern big jet' engine spools down in 3 seconds and how long it takes to return to full thrust if the thrust lever is advanced at second 4. (And by 'modern big jet' I don't mean a B707...).