We have recently prepared our save the date cards and have begun to hear that some relatives cannot come as they will be out of state at that time of year. Do we still send an invitations if guests reply with regrets, when they receive the save the date?

I say yes just incase they don't end up going out of state. Things happen and plans change.

I would say send them, let them know that you hope too see them there but if they can't make it that is okay too.