That's an assumption. It did not "have to" occur prior to impact. It could have occurred upon impact and those components could have ricocheted off the tree (or a kerb or any other deflector) back along the path.
Also photos appear to indicate the car didn’t crash into the palm tree but came to rest against the palm tree.
A still photo taken after the fact, by its very nature, cannot demonstrate that to be the case.
Laws of physics would dictate the engine assembly could not have separated as a result of impact with the tree given the engine’s location.
Which laws are those, now, specifically?
If so, it would have continued on in the direction of travel at the point of impact
Unless it hit something, like a sturdy tree, in which case it would not have.
the crash scene bears little resemblence to a simple head on collision
The photos do not show that it was a head-on, 90 degree angle collision.
I don't think anyone is claiming that this was a "simple head on" collision.
The simple laws of mechanics, motion and kinetic energy. For the car to have impacted a stationary object and then have an assembly as massive as the drivetrain to reverse direction and end up 150-200ft behind the car is impossible.
The entire drivetrain would have had to reverse direction through the firewall and passenger compartment and then have the energy to travel the 150-200 ft against the direction of travel. Still photos do indicate the type of front end collision necessary to even approach that type of event and generate that level of kinetic energy simply did not occur.