If i take immunosuppressants after an organ transplant will my immune system be severely compromised in the long term to the extent where flu kills?

No, but: it depends on your condition before and after transplant. In general, avoid getting in contact with people with colds/flu and crowded places if you can,wear a mask if you have to,report any fever or illness to your doctors, unlike others you may be put on antibiotics early in the course of fever,you will need some more vaccines such as pneumovax, otherwise you have a normal life, wish you wellnes