Applescript - Image Renaming, if error write filename to a text file

Hi there, I have the following script

set excelFile to choose file with prompt "Choose the Excel file" of type {"XLS6", "XLS7", "XLS8"}
set theFolder to choose folder with prompt "Choose the folder containing the files to rename"
tell application "Microsoft Excel"
	open excelFile as text
	tell active sheet to set P to value of used range
end tell

set {fileNames, EAN} to {{}, {}}
repeat with i in P
	set end of fileNames to item 1 of i
	set end of EAN to item 2 of i
end repeat
set theFiles to list folder theFolder without invisibles

repeat with oneFile in theFiles
	set idx to BinarySearch(fileNames, contents of oneFile)
	set x to item idx of EAN
	tell application "Finder" to set name of file oneFile of folder theFolder to item idx of EAN
end repeat

on BinarySearch(theList, theValue)
	script o
		property l : theList
	end script
	
	set low to 1
	set high to (count theList)
	repeat until (low = high)
		set mid to (low + high) div 2
		if ({theValue} is in items low thru mid of o's l) then
			set high to mid
		else
			set low to mid + 1
		end if
	end repeat
	
	if (item low of o's l is theValue) then return low
	return false
end BinarySearch

Which works perfectly on small numbers. However we are going to renaming some 8000+ files and there are bound to be one of two files that don’t exist. So, if the file does not exist can it write that filename to a text file and carry on?