V1 is only designed for a single engine failure descisions. All the other scenario's are up to you and me but it helps if you realise that beyond it, with all the braking you can do, you may still run out of runway before you run out of speed.
Q a. is simple:
1 - I get a red light right in front of me.
2 - I get a fire bell disturbing the serene silence of a T/O.
3 - I am trained to reject on a fire warning before V1.
4 - I have very little time to look around and decide what kind of fire this is.
I think I'll stop.
Q b. is just a little bit harder. As a PF I am mainly looking outside; especially in a low vis T/O. So with some luck I'll just hear some clicks behind the F/O's C/B panel accompanied by an amber master caution light on the lower end of my view. This will, of course, not cause me to reject. If however I happen to see my complete EHSI gone during a quick glance at the speed, or most of the eng indications missing, or my F/O screaming for help I could decide to stop.
Of course de choices made by Mustafa are the best ones in retrospect. Procedures are not always the best solution for every possible or impossible scenario. They are supposed to be the best average.
ACARS, The point of V1 is that you are supposed to have too little height over the fence at the end of the runway if you lose an engine before it and beyond it you are supposed to be left with too little runway to come to a stop on the concrete. All this is on the assumption that during a reject all the other systems are working (like e.g. your brakes) and after V1 all systems you need for flying are working (like your flight controls). Now the fun really starts if you reject
a) before V1 and find out that this blown tire ruptured some of your brake lines or
b) you continue after V1 and that find out these birds did not hit one but two engines.
Sometimes you win, sometimes you loose.
Sq