Why should it be desastrous? I hope you do know the odds.
The COVID-19 fatality odd is 0.3%, the Dragon-lost odd probably much higher, maybe at around 5%. The Falcon 9 has over 80 starts now, but this is only the 3nd Dragon 2 start, and one of it failed.
I think the astronauts health makes them much less likely to die from Corona than 0.3% but exposing the current crew of the IIS does not sound like a good idea either.
Fatality rate is one thing, but being in a small space can cause high concentrations of virus and any health complication in space is a big deal.
A catastrophic failure is definitely a risk, but not sure how its magnitude should diminish our caution when it comes to bringing the virus to the space station (by your calc, it lowers the risk only by 5%).
The COVID-19 fatality odd is 0.3%, the Dragon-lost odd probably much higher, maybe at around 5%. The Falcon 9 has over 80 starts now, but this is only the 3nd Dragon 2 start, and one of it failed.