Are you from Czech Republic? If yes, can you send me your mail? :-)
Why not connect all N of the switches parallelly to the light and still use scenes? This way, all of the switches would work if there is no WiFi...
@Srdan: That would work but would require new wiring installed in the walls. It would be best to have a way of retrofitting smart switches that uses traditional wiring in the walls for 2-way switches or bypasses the wiring requirement all together.
The software solution using scenes works well but there is the limit of 21 scenes so the limit of 10 switches in a whole house. I reached this limit and I still missing the 3 bedrooms with 9 switches.