Instead of cancelling, can we find an indoor space to meet?
Some indoor spaces:
Boston Public Library
One of the many food courts around: City Place, Quincy Market, South Station, Museum of Science, Cambridgeside Galleria, Prudential Center(?)
A building atrium
A hotel lobby
Some area on an open-campus college, like MIT or Harvard, don't know about BU or Emerson
I'm not familiar with the library, so I suggest
City Place. It's just south of the Common, with an alleyway entrance across the street from the burial grounds.
CommonCents, what do you think?