What should happen to funds when a congregation closes?

Answer:

It should be remembered that the funds that a congregation has belong to God and not the members of a congregation. This is implied when Ananias was told that any money he had was his to do with as he desired, but once it is given to the church those funds are now God's (Acts 5:3-4). Therefore, any remaining funds should be used to accomplish God's work.

What commonly happens is that remaining funds are distributed among preachers that the members know need support. Lacking that, some congregations turn their remaining funds over to neighboring congregations who will then put the funds to appropriate use.