Litecoin wallet backup

Hey Joe,really good video thank you for that. I have however one question
that I can’t seem to find the answer to. A lot of websites say that before
you backup you have to let your wallet completely synchronize. Let’s say I
do that,and then store my backup wallet.dat file offline,and then delete
the wallet.dat file from my computer for security. Won’t my wallet.dat file
become “outdated”? I’m kinda in the woods here,would be great if you could
be of any help