There are different kinds of NOC...you have to know what kind of NOC you are getting. If they gave you a NOC for entering Qatar, then your husband CAN come back to Qatar, but CAN'T work or be sponsored by another company. If the NOC they gave you mentioned that they don't have any problem if he'll work with another company, he can work, provided that the VISA that the old company gave is still valid, otherwise, he has to exit and buy/get another VISA, either Family or Business, but not a working VISA. If the NOC states that they have no objection to transfer sponsorship, then that's as good as being released.
There are different kinds of NOC...you have to know what kind of NOC you are getting. If they gave you a NOC for entering Qatar, then your husband CAN come back to Qatar, but CAN'T work or be sponsored by another company. If the NOC they gave you mentioned that they don't have any problem if he'll work with another company, he can work, provided that the VISA that the old company gave is still valid, otherwise, he has to exit and buy/get another VISA, either Family or Business, but not a working VISA. If the NOC states that they have no objection to transfer sponsorship, then that's as good as being released.
just my 2 cents.
Coelacanth