7 people on one PNR, one no-show
 

I have a trip coming up later this week with a group. There are seven of us on the single PNR, and we know that one of the group is not going to be taking the trip. Should I call up and have them split from the rest of the group, or is this not going to cause any problem? If it makes a difference, this is an international trip (Mexico). Thanks.

Unless you know absolutely 100% that person is not traveling with you I would hold off on splitting the PNR. Call CO just before the OLCI window and do it then. Once the PNR is split it cannot be undone.

Spliting a PNR can be done at any time. It's always better to have this done before OLCI just to avoid checking in the person by mistake.

Is the person going to use the ticket for anything else? If the change fee is >= the ticket price, don't even bother, and just check him in. There's a chance (albeit a small one), he'll get the miles.