I've never used the loner trait, except at the first as it was suggested for authors. I don't really like it, but that is due to I think that I am a people person in real life so it feels abnormal.
As MoMoll stated, getting them to talk on the phone can take care of the problem. With my family oriented sims, they can have a hard time in other countries due to lack of social interactions; and I so far haven't done any tomb exploring yet.
But, when it gets low, and it has gotten quite low a couple times, I had them call home and in no time it was full. Had one on top of a hill and was very loney, so had him call home and after a chat with wife, he was as happy as a lark.