kwiringira bruce herve The post about ExitNFT is giving an idea of how it will underneath. Matic will provide a way to do it automagically using Matic Wallet. Non-tech savvy users never have to worry about the complexity of it.
Regarding security, this ExitNFT mostly needs an underwriter who claims that exit valid. If underwriter sends those tokens to Exitor and realizes it was not valid exit, they suffer the loss, not Sidechain.
Anyone can become an underwriter. And again, Matic will hide this complexity under the hood.