My approach would be:
(a) clone the whole of that USB disk (with the deleted partition) to somewhere else (so you need free space of the whole capacity of your problem disk, unless using compression during cloning), using a raw/whole disk type of cloning utility (
not the default settings of Ghost/Acronis etc. as those will try to clone only filesystems, unless the settings are changed).
(b) once you have that backup copy of the problem disk, you can try one of several partition-finding utilities (e.g. testdisk) on that disk, and if they screw up your disk completely (which can happen), then you just restore back from your clone of the problem disk and try a different utility.
Some people may say that taking the initial clone is not needed - but those are the people who haven't seen the "partition-finding" utilities make a complete mess of the disk they have been run on.

As always, DIY has risks (human error, equipment failure, software bug etc. etc.) so you have to recognise your limits and decide for yourself what you are capable of doing, and what risks you are happy taking. Your data, your risk, your choice.
Good luck!