Define the purpose of these components in the operation of this low side driver
C1 helps keep Q1 from turning off too fast.  D2 may not be enough to prevent the inductive kickback from harming the driver.  Stopping current through an inductor more slowly limits the peak voltages produced.  R2 helps pull the base of Q1 down so it can turn off completely since D1 prevents the driver from sinking any current from the base.  D1 further protects the driver from voltage spikes, as well as providing a bit of voltage drop between the driver and the darlington so it doesn't conduct when it is supposed to be off. (As per SteveSh's comment, the 7407 may have up to 0.7 V on it's output when off).

A blown driver.

They should stay unchanged.  If the MCU is not open collector (push-pull, for instance, which is common in MCUs) you will need a series resistor to limit the current.