As an ex-cop I had the horrific experience of attending railway fatalities usually if it was a suicidal person the police were actively looking for - most deaths on lines are people who sadly feel their lives are not worth living anymore.
Generally if a fatality does occur, it is treated as a crime scene with forensics taking photographic evidence. This is not necessarily because someone is to blame and the powers that be are wanting a scapegoat. It is done to secure evidence for the coroner when an inquest takes place.
From my own experience, the body is generally removed by duty undertakers who will attend the scene. Without sounding too graphic, if the body of the deceased is not intact, then forensic scientists together with pathologists will help remove key parts. A police search team usually working with track operatives from Network Rail will conduct a full speculative search of the track for further evidence of body tissue or any disgarded personal items like wrist watches, wallets, mobile phones if anything is left in tact. Once the investigation team has been stood down, the track workers will get authorisation to clean any extensive blood loss or tissue with full cleaning equipment so train services on the line can resume.
As for train staff (drivers, conductors, train managers) from my knowledge, you are removed from the scene along with the passengers once it is safe to do so. I'm not too sure if drivers have to provide statements to the police - it is extremely traumatic for any driver and I'm sure there will be regulations in place layed down by the Unions which protects the drivers but I would still think drivers will have to provide some sort of routine report to a line manager. As I wasn't British Transport Police I can't state what the exact procedure is for drivers giving their account to police.
I am lead to believe some train drivers can go a full thirty years without experiencing a death on the line while other drivers are sadly unfortunate to experience two or more deaths during their career.
One suicide is one to many in my opinion - it devastates love one's, railway staff and people like me who had to deal with the aftermath more than once.
Like another member has said - a bus driver or HGV driver are more likely to be faced with a fatality so please don't let it put you off a rewarding career in the rail industry.