popatim :
You said it had important files on it... not 'copies' of important files
Never trust one device to hold your important files. Having multiple copies is the only way to survive a drive failure. While your drive is working fine often there are no warning signs to predict when it will fail.
So please get another drive or something just to have a backup of those important files.
Hmm..
I'd assumed he'd backed the files up as well but it's not clear.
So YES, if your important files are only on the USB drive copy them to your main drive or make other arrangements to ensure you have at least two sets of files. For pictures I recommend putting those on DVD as well, possibly Millienata M-Disc.
Another option if you don't mind the cost is to get one of the Western Digital Duo drives that is connected to your network. Get a 4TB version say and make sure it's in RAID1 mode so your data is on both drives. If it detects a bad drive you can swap drives and it auto rebuilds the RAID.