The class is cancelled and the book will probably be delayed too.
This doesn't seem to have actually been the case: https://groups.csail.mit.edu/mac/users/gjs/6.945/ There was an individual class meeting that seems to have been canceled so perhaps you were referring to that. Also even if the class was canceled the book being delayed would depend on whether or not the book was not to be released until fall due to inadequate testing or some other constraint. Regardless I think we can remain hopeful for a fall release.