In message , Paul Corfield
writes

The Northern Line has tended to run an OK service on strike days but it
will be busy at either Charing Cross, Waterloo or London Bridge.

TfL have already announced that Charing Cross tube station will be
closed throughout the whole of Monday. They expect all lines except the
Circle to be running in Zone 1, so changing to the Northern at Waterloo
East might be an option, but the crowds will be horrendous and TfL's
plans could change (even though I agree that past experience suggests
that some sort of service will be maintained on the Northern).

I basically concur with the advice to head for Charing Cross and then
assess options from there.

Me too. If the buses are impossible and walking is not an option,
there's always the option of a taxi - on strike days, it's common for
people in the taxi queue to ask if anyone wants to share a cab to a
major destination such as Euston.

--
Paul Terry