Usually when the HPFP dies, they just die, and the engine will not run.
You may have gotten lucky and yours is just starting to come apart, or there is some other issue.
I would first open up the fuel filter canister, and look closely for any metal shiny bits inside. If you find any, problem found, you need a HPFP and related stuff. You *may* get lucky and your injectors are still OK, I have never seen that happen though.
If you do not see anything there, I would check the actual and requested rail pressure, as well as the connections on the N276 pressure regulating valve (which is on the flywheel end of the fuel rail) and the G247 rail pressure sensor.
You can also take the N290 fuel metering valve off of the HPFP and see if it has any metal debris trapped in it, as well as the G247.
That is for the P0087 low rail pressure.
The P047A is for the #2 exhaust pressure sensor, and that is unlikely to have any effect on how the engine starts and runs. I would consider that a second issue at this point, as it is most likely just the sensor and not a big deal at all. The HPFP is a big deal.