Dominant,
I sympathize completely as I have a USB 2. Western Digital Passport 320Gb and which has been a nightmare nearly from the beginning. These are dangerous devices in my view as they seem to work- be recognized- sometimes, stop working, and then work again. Currently, one partition of this drive can be seen and the other is invisible.
I'm not clear on the details of the failure. You mention the "boot sector"- was this configured as a boot drive?
In some cases, changing partitions by merging- rather than resizing- can wipe off the data, but the new space should be recognized regardless as even if it is unallocated. If it was a boot drive, but the boot sector is corrupted or removed, you might try EaseUs Partition Master (free) and see if it will recognize the drive and show the volumes. Be ready to copy the data at any time onto another drive as knowing these drives, there may not be another chance.
My only other advice is to try the technique that worked for me, which is to try the drive on every USB port on every computer with which you have access. My drive only works on one partition on the left front port of my Dell Precision T5400 - that system has 10 ports, and not at all on my HP z420 which has 10 ports both USB 2 and 3. Some people have commented that the ports closest to the motherboard are the best bet !
Sorry, I can't be more informative. I trusted this drive one time too many and I've had enough of the horrible uncertainty of the Passport. If I can ever recover the data from the missing partition, a half hour later I will create a video of running over this drive at 65mph with a 1970 Mercedes 300SEL 6.3L- my heaviest car. Knowing the Passport, it'll ruin an expensive VR tire,...
I've gone back to the external drives that have been perfectly reliable- a 3.5" drive in a enclosure having a power switch and a cooling fan. I run these only when backing up or making transfers larger than my flash drives and the drives last forever. I have a Seagate 160GB that is seven years old- perfect reliability. My new one is a Star Tech USB 3 (about $40) with power switch and switchable fan to which I added a Seagate 500Gb 1BD142 drive and I've seen sustained copy at 170MB/s. So far so good, but I back up to both the old and new Seagate and Star Tech for now.
Let us know what you discover. If you look around on this forum and the Intertubes in general, there are many many horror stories about these sometimes drives.
Cheers,
BambiBoom