QUESTION:
Could the heat shield, the backshell or the parachute come into contact with
the lander inadvertently?

ANSWER from David Dubov:
Another good question. There are two parts to your question.

For the problem of "recontact", we spent a lot of effort to make sure that
recontact does not occur after separation. We did this in two ways. First we
spent a good deal of effort to create models (mathematical/computer ones) of
most of the components (including the parachute). We characterized the
forces of things like the separation springs, aerodynamics and gravity,
measured clearances and mass properties, determined the quantitative
uncertainty in these parameters (tolerances), and finally we simulated the
separation events over and over again using the full range of possible
uncertainties - guaranteeing that recontact does not occur in any of the
possible cases. So that we could double check that our models were created
correctly, we then do a small number of separation tests using real hardware
and confirm that the model correctly predicts the outcomes for the test.
This latter step is what we call "model correlation". If this all sounds
like a lot of work, rest assured that it is! This is why making spacecraft
isn't cheap.

The other part of the problem is in what happens to the backshell, parachute
and heatshield after separation. In the case of the heatshield, we know that
it will hit the ground before the lander and a long way away (it separates
when the lander is miles above the surface). In the case of the backshell,
we ensure that the rockets are still firing when the bridle is cut at the
lander. The residual rocket impulse pops the backshell up and away at up to
100 m/s (225 mph). It will go up in a long arc because the center of mass of
the backshell is slightly offset. Since the parachute stays with the
backshell as it pops up, it too will sail away from the lander. From the
lander's cameras, we hope to be able to see the backshell and the parchute
in the distance after we land.