  Recent detailed 1D core-collapse simulations have brought new insights on the
final fate of massive stars, which are in contrast to commonly used parametric
prescriptions. In this work, we explore the implications of these results to
the formation of coalescing black-hole (BH) - neutron-star (NS) binaries, such
as the candidate event GW190426_152155 reported in GWTC-2. Furthermore, we
investigate the effects of natal kicks and the NS's radius on the synthesis of
such systems and potential electromagnetic counterparts linked to them.
Synthetic models based on detailed core-collapse simulations result in an
increased merger detection rate of BH-NS systems ($\sim 2.3$ yr$^{-1}$), 5 to
10 times larger than the predictions of "standard" parametric prescriptions.
This is primarily due to the formation of low-mass BH via direct collapse, and
hence no natal kicks, favored by the detailed simulations. The fraction of
observed systems that will produce an electromagnetic counterpart, with the
detailed supernova engine, ranges from $2$-$25$%, depending on uncertainties in
the NS equation of state. Notably, in most merging systems with electromagnetic
counterparts, the NS is the first-born compact object, as long as the NS's
radius is $\lesssim 12\,\mathrm{km}$. Furthermore, core-collapse models that
predict the formation of low-mass BHs with negligible natal kicks increase the
detection rate of GW190426_152155-like events to $\sim 0.6 \, $yr$^{-1}$; with
an associated probability of electromagnetic counterpart $\leq 10$% for all
supernova engines. However, increasing the production of direct-collapse
low-mass BHs also increases the synthesis of binary BHs, over-predicting their
measured local merger density rate. In all cases, models based on detailed
core-collapse simulation predict a ratio of BH-NSs to binary BHs merger rate
density that is at least twice as high as other prescriptions.
