What an interesting thread this has turned into.
So, let's start from the beginning?
Man climbs to the top of a semiphore signal at the end of Platform 1 facing North, which is a standard trespass incident; run no trains through the platforms until he is down, detained by BTP, area searched and he is off the station.
Added complication in that the man is mentally ill, has a knife, has already self harmed himself and is covered in blood. What's the main concern? The people trying to get him down and the passengers (innocent joe public). So, station is evacuated, fine. Specialist negotiators brought in as per procedure, nothing else happens, man gets tazered and falls to platform with neck injuries.
Trains are held on both up and down lines, again fine as standard. Bearing in mind Chiltern Control is round the back of Banbury Station and can see everything going on by CCTV etc.
The train held in question for 4 hours were on about here, refreshments were given out by the onboard crew but these run out. It was just north of Banbury - however no where near a safe spot, could probably walked to the station yes, but it would of been past the knife welding man.
Turning it round to Leamington, then putting passengers on buses would of taken quite long as it would of run at a reduced speed.
Between Banbury and Leam, isn't near any main roads with taxis and buses running along side it so your argument is invalid and the terrain is quite horrendous for a train packed full of commuters to get out into without landing in fields full of all sorts of surprises.
Yes quite an inconvenient length of time, but sat on a clubman where I'm safe from being run down or stabbed is a sensible choice I'd like to think.
I'm confident Banbury is being resignalled in the near future to rid the Semiphores so climbing up them won't be an option...