But sadly the 7 gig isn't enough for construct the .deb file as you said, it failed in the middle of the process filling up the disk.
Before anything else, you should delete the temporary ./play.it directories, that should be in either /tmp/play.it or the directory you specified with TMPDIR. For easier debugging, they are not automaticlly deleted if something failed in the package building process.
Then, there is still something you can try ;)
A couple things actually…
Building compressed packages, so they will take less disk space at the cost of longer building and installation times:
./play-vampire-the-masquerade-bloodlines.sh --skip-free-space-check --compression xz
Moving the GOG installer to an external storage like a USB stick, and still run the script from your system, giving it the path to the main installer part:
./play-vampire-the-masquerade-bloodlines.sh --skip-free-space-check /media/usb0/setup_vampire_the_masquerade_-_bloodlines_1.2_\(up_10.0\)_\(22135\).exe
Moving the GOG installer to an external storage and run the script from the external storage device, so the final .deb packages will be put on it too. If you do so, make sure to *not* set TMPDIR to some place on your system disk, not the external storage, or you will get issues with file permissions.