I've never heard of this med being associated with dementia or with lowering the immune system. If your withdrawal persists, go back on the med at the last dose at which you felt fine and then taper off slowly, as you should have done. If you ever go back on benzos, know that quitting abruptly can cause seizures.
I don't think you have any memory loss to fear after just 44 days, but if you can't get over the fears then you should talk all of these fears over with your pharmacist or doctor, Many people take this drug yet its usage isn't listed as a leading cause of dementia, so likely the chances of anyone suffering damage after such a short time on it is near zero.