Just 2 suppositions to rescue the trapped family:

1. use a teleporter to conjure the sims out and move-in them with yet another lot with a family or a single sims. Then, move out the dummy sims.

2.
When you dump the lot into the lot bin, the family should be modified around the same time a the lot, so the family files can be found and located.

the next can be tried is file replacement.

may try to make a lot of the same size and dump in a dummy family with similar sims F/M, ages.
Then, use a copy of the family found in the LotCatalog folder to replace the that lot's family.


related thread:
http://simpeforum.ambertation.de/si...-a-Lot-Plz-help
http://simpeforum.ambertation.de/forum/viewthread/4448
http://www.modthesims2.com/showpost...7&postcount=360
http://www.modthesims2.com/member/s...01&postcount=13

The lastly linked method can at least work for my lots without a family.

Potential problems:
1. personality and some sims infos may need some readjustments afterwards.
2. it doesn't work, but it doesn't matter since dummy copies are used.