I flew LHR-HND on JAL this week and sat beside a couple in the lounge in HND who'd been booked on NH212 the same day, which of course was not operating. They'd been rebooked on LH- LHR-FRA and NH FRA-HND and arrived in HND at 8 am. So this would leave you a huge amount of time for your transfer, but checking luggage all the way through from LHR would be now up to LH check in, not NH.

I'd be very surprised if the LHR flights continue to be cancelled indefinitely but I can't see anyone flying over Siberia anytime soon.