Letters
If one is familar with and uses the church family books, you can note many of those who left there, it details in the 2nd from right column on the right page where they went, even if it was to America or another village . . . granted not all are documented there, but many are . . . anyone who has not pulled their own family data from the chruch family books for the families they are researching has not even started good on their family research - IF there are family books for their villages.
http://pixel.cs.vt.edu/library/bess/bessind/
Next is the EWZ and the Koblenz records, there is often data there for many people that is worthy to chase down. The Bessarabian researcher must use the Koblenz index data as it becomes available, and much more is in the cue for posting and much more is being prepared;
http://pixel.cs.vt.edu/library/war/ewz/
http://pixel.cs.vt.edu/library/bess/koblenz/
One thing to note about all that we point to here is that these are index data and are provided as a finding aid for the reseacher to find their own data and study it - there might be some notes that says "to America" in some of the index data such as these;
FUELLER Johannes 1865 67 140 299 1768281 2 Borodino to Amerika 1893
HOEGER Georg 1861 299 26 1768282 1 Borodino to Amerika 1889
If I understand the focus of the core question here correctly the passport and traveling papers that the folks brought with them that hopefully is being held by somebody in the family circle is the prime items to go looking for and trying to seek out . . .