I agree with this answer about not telling the client directly about your resignation from a consulting company. However, I am now facing a peculiar situation related to this.
I work for a consulting company A, and have been deputed to work for their client company B. I offered my resignation to my manager in company A about a week ago, and assumed that, as per the protocol, they would communicate it to the powers-that-be in company B.
I am now noticing that my company A hasn't informed company B. Someone from company B has asked me for a meeting to plan how we would work on a milestone, which is due on a date X, one month after my resignation date Y.
This puts me in a dilemma. It would be unprofessional (and possibly, illegal) to commit my time until date X, when I already know that I am only available till date Y. However, I also cannot tell them that I am only available till date Y, without telling why.
Of course, the "obvious" approach is to ask my company A manager to deal with it, but he doesn't work on-site at this client office, and is unreachable. I have been able to procrastinate the meeting for a day, but obviously, I cannot keep stalling this forever.
What would be the most professional way to handle this kind of situation, without creating problems for either company A, B, or myself?