Maybe:

In case we don't talk anymore before the holidays, I wish you a Merry Christmas and a Happy New Year!

Natürlich kommt es darauf an mit wem man spricht (Religion, etc.).

I would prefer to say:

In case we don't hearing from each other...

@kyle91,

ich glaube "... we don't hearing ..." geht gar nicht im Englischen, so weit ich weiss.

evtl.: "... we don't hear ..."

Ups, you're right. You have to use the infinitive.

But if the persons are face to face it might be better to say:

In case we don't see each other befor christmas...

'before' of course with an 'e' at the end