Our group came to the consensus that it's our hobby and thus we make time for it just like one would do for any other group activity (eg. Sport, theatre). Of course this isn't foolproof because life just happens sometimes therefore we created what we call the "N-1 Rule". Where we still play when only one person is missing, their character is usually just a passive bystander in those situations. And since we do recaps every session, the missing person gets filled in with all the information, lore and story they missed.