I think you will have to use VB(A) to reconnect to the datasource to be
sure - generally speaking Word uses an absolute pathname. It /may/ connect
to the file in the same directory in some circumstances but I wouldn't want
to rely on it.

As a rule if you are moving things around you should turn your mail merge
main document back into a "Normal" Word document before moving it. If you
don't, users will almost certainly see the "Cannot find data source"
message. The document should retain its field codes, but it will lose
a. the connection tot the data source
b. the mail merge type (Form Letters, Catalog/Directory etc.)
c. the mail merge destination
d. filter and sort options

So in other words any VB(A) you use will need to restore all those things.