RedBaron
The rules in the tariff T654 are the following:
3.1.1.3 Any contracting party domiciled in Switzerland, Germany, France, Italy, Austria, or the Principality of Liechtenstein concludes the contract with automatic renewal. Other contracting parties obtain an annual subscription without automatic renewal. (Google translation)
But if you leave Switzerland to a non-neighbouring country, you must certainly inform SBB about your change of address and indicate that you want to cancel the suscription.