A normal ticket is for a route, so with a normal Zermatt t0 Zurich ticket you can indeed break your trip in Bern, and continue later.
A supersaver ticket however is not flexible, there you need to take the train you selected.
When booked sufficiently in advance the cheapest option on Zermatt - Zurich is often a Saver Day Pass, which is completely flexible, and even gives you unlimited travel on the buses and trams in Bern itself.