Based on 3 dreams and a vision received by Dumitru Duduman,

the final page of the Book of the Gentiles will be filled at some point in time.

Dumitru Duduman was told in dreams and a vision he received that:

A.  Before this book is completed, "Some of the names that are listed here will be erased. [See alluding to "blot out" [erase] in Rev 3:5.]  I will erase the names of those who have
 
mocked God [Gal 6:7] [Heb 10:29(26-31)] and

tested [Luk 4:12(9-13)] the Spirit of Grace [Heb 10:29].
 

I will replace them with other names."  [dream text]
 
This suggests that, just as we are free to choose salvation by asking Jesus Christ to be our Saviour and Lord, we are also free to renounce our salvation by mocking God and if we sin willfully (if we deliberately keep on sinning (NIV)) after we have received the knowledge of the truth (Heb 10:26-31).
 
B.  "When these pages are filled, The Grace will leave the gentiles."  [dream text]
 
This is likely an immediate result of the book being completed.
 
C.  "When the total number of the gentiles is completed, the writing in this book will be finished."  [dream text]
 
Apparently, no more gentiles will be saved after this book is completed.  This would mean that born again Christians, whose names have not been erased, must still overcome and endure (Mat 24:13), during the 3.5 year Great Tribulation, until the Pre Wrath Rapture (see Rev 7:9-17), and new born-again Christians thereafter, until the earth is reaped (Rev 14:14-16).
 
D.   Before this book is completed, "I still have names to add to the number before all the things that I have shown you will happen."  [vision text]
 
All the things happen in their prescribed sequence after the book is completed, but not necessarily all at once.
 
E.  "When this is completed, what I have told you will happen to America."  [vision text]
 
Based on other prophecies given to Dumitru Duduman, this is not likely to be an immediate result of the book being completed, but rather that sometime after the book is completed, the foretold event can and will happen to America.
(Notice the 2nd use of the word "before" in "D." above.)

Since Angel#1 (of the 3 Angels in the book of Revelation) preaching the gospel is likely the final call (to those still living) to accept Jesus Christ as Lord and Saviour,

and since Angel#2 proclaims that Babylon has fallen (what "will happen to America"), the Book of the Gentiles is probably completed, and The Grace will leave the gentiles, sometime between Angel#1 (Rev 14:6-7) and Angel#2 (Rev 14:8 and Rev 18).   ^    ^