what if they release his luggage and he will have to get another boarding pass for the connecting flight?
my understanding was that he will come out through immigration and customs and will check in again(different airlines), in this case he is coming out of the airport and actually entering the country, but if there is any law or special permission regarding this then I may be wrong!
Normally, if you buy one ticket from your point of origin to your destination, when there are connections the luggage gets checked all the way through to the end destination. I know this may not be the case in all countries (USA) but for most in Europe it is. It's where you buy more than one ticket that problems with luggage can occur if you are not able to check in again. For people not allowed to leave the secure area, they will usually be escorted to clear immigration and to the connecting gate/terminal if required. I know that happens in most European airports but can't say for all. But it is at the discretion of the immigration officer in the connecting country. That officer CAN allow them to leave the secure area if they believe strongly that they will not stay in that country and continue on to their end destination.
It's not a law but LAWS and agreements between countries to facilitate travel.