Hi MAAZ,
To explain the 'post procedure' I'll stick with the example of YSSY34R Marub 5 departure. Keep in mind that the Obstacle clearance procedure (OCP) and 'post' procedure are NOT published on the chart because they are aircraft dependant. In our case we use Airbus 'Flysmart' data which for each runway will show these on our iPads.
Luckily, this is not some sort of intuitive thing that you'll need to 'feel in your waters' on the day. You will do ONE of two things:
1) Should you lose an engine between V1 and 500 feet then you will follow the OCP which states that we maintain runway track of 335 and then at 10DME SY we turn right and track 090 degrees climbing to the MSA or until radar is happy to give us radar terrain vectors.
2) Should we lose an engine at anytime after 500 feet then we do not have any option but to commence the 'post' (after the first SID turn) procedure which in this case is to turn right and track 090.
The aim on this chart is to avoid bumping in the Sydney central business district including counterpoint tower. (C) marks the spot and (P) marks the post procedure or what we would do after we have already started the turn.
Prior to takeoff, all options are accounted for and understood as standard procedure. The only ambiguity will arise when you have a stalling or vibrating engine in which case once the initial startle factor subsides you will need to do what is most conservative. For my money in the above example, My clients would wish for me to do one of the two above options simply dependent on whether or not I had stared the turn. That is to say whether I am before or post the initial SID turn.
I hope that makes sense.