It has been 2 years since I downloaded GW2 and the Gw2.dat file zise is now 24.4 GB (26,280,349,560 bytes), will the file become smaller if I delete the all the game and download it again?
Dunno, wiki says it might do so. :/ This is my dat. I have had GW2 in this folder since first beta.
Gw2.dat wiki
The file Gw2.dat is a compressed archive file that contains all data that is required to run Guild Wars 2.
To save time in-game, it is possible to have the client download all available data on startup using the -image command line argument. It is also possible to copy the Gw2.dat file to another machine to avoid having to download all the files again.
Notes
The file size of your Gw2.dat might not be the same as someone else's. Since the file is created and modified by adding and changing files inside of it dynamically, its size and CRC will vary in different installations of the game. Also, many files are downloaded in a compressed format and will only be decompressed when you encounter them in-game.
To install the game on multiple computers, it is possible to just copy this file and the Gw2.exe file into the same folder, instead of having to download the game again on each computer.