With all insurance policies here, if you can prove you don't need them any longer you can get most of your money refunded. However many policies tie you in to a 10 year contract, but if you leave Switzerland or sell the van you get a refund. Handing the plates back stops the insurance running, but there is usually a SFr 50,-- handling fee.
You must, before you sign any contract, understand what you are signing up to, and if you don't like one of the conditions get it removed.
I crossed out the automatic annual renewal clause on my Fitness center contract. They said they couldn't agree to that. I walked away. They called me back and agreed to a 12 month clause.
I found out that the TCS insurance is on a 12 month renewable basis, web page is only in D/F/I and I think the company behind the TCS offer is the Basler Insurance, and therefore can be reccommended, (but you have to join the TCS, membership is Fr 90,-- per year):
http://www.tcs.ch/main/de/home/versicherungen.html
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