This question is likely to be closed as opinion-based, but some reference points:
Unless things become positively apocalyptic exceedingly Japan's airports are unlikely to be completely closed. Flights could be reduced, but as a point of comparison, airports in China – even in Wuhan – continued to operate there throughout the crisis.
On the inbound flight, this would require an infected person from Munich or London, which is statistically unlikely. On the way back, this is more likely, but still unlikely, unless (again) there is a major outbreak.
FWIW, I was in Tokyo last week and although there isn't a lot of panic in the air, people are definitely taking precautions: temperature scans at the airport, more masks than usual, hand washing and disinfectants, large gatherings canceled etc. This in itself seems to be the spread of the To limit the virus, making complete infection less likely. But at the end of the day, it's your call.