What do you do when members make pledges to a building fund and then leave the church before satisfying the pledge? Some say "sue". Some say "forget it". What do you say?
As a christian you should forgive, however it would be good stewardship to visit, call and/or send a note asking if they will be fulfilling their obligation.
The key is to do it in love, and if they do not plan on fulfilling it to make note of it for tracking.
Pray for them and forgive and forget. It is truthfully between them and God.