Maybe someone had such an experience...

we lived in our rented flat in Zurich for 4 years (not Swiss citizens, just working tehre). now we are moving to Germany close to Zurich, but would like to keep the flat at least for 1 more year. Is it possible? when we move to another country we will have to return our swiss permits, etc.

we would prefer to sublet the flat (maybe for short periods like 3mnth+3...) until our renting period reaches 5 years, then we dont have to repair everything + my husband is doing some small jobs in Zurich and it would be nice to have a bed to sleep in Zuri sometimes. we also missed the notice period already as we move out in 1.5 months!

would it work if we just move another person there without notice to our landlord and we will continue paying our bills as usual? or is it risky in any sense?

its possible but has to be made officially.
It's called sub-letting and you need to inform the agency or landlord-

If you plan to do that, you can't put the rent higher than your's now- but you can make a separate contract to rent your furniture.

That's it-
I heard many people in Switzerland do that to secure their flats...