Actually you have a double edged sword here. Yes you must tell them but if you don't then they need to find out which is far from easy IF you have an address here. If not then you can easily run into a problem. So the question you have is have you deregistered from your gemeinde? If so then where will you register and when - very officially there cannot be a gap of more than 7 days here.

If you go to your gemeinde and tell them you are going on a world cruise for 6 months they will say okay fine as long as they know...

So do you want to keep your C permit? IF yes talk to your Gemeinde it will save a lot of potential problems in the future... And yes then you can take up to 2 years out of CH without any hassle...

So Gav do yourself a favour and spend ten minutes telling them you are going to "find yourself" for the next 6 months picking fruit even if it is bullshit...