Am I over-reacting? Found out my director/ line manager is being replaced from the 'all staff' email.

Feel completely deflated right now, found out last thing today, in the usual happy-clappy HR email that my line manager is moving to another department, yay for them.

No mention in the email what happens to the people that report to them, no-one's mentioned it to me. I assume I just carry on until they hire someone, but am I right to think this is a really abysmal way to manage something like this?