Hey! Biomedical science has many possible outcomes:
- Some people go on to do postgraduate medicine
- Some people go on to do other postgraduate study, such as an MBiomedSc, PhD, MPH etc.
- Some people enter the workforce in some capacity, either as a researcher or working in a lab (be it commercial or otherwise)
Biomedical science is a broad and growing general discipline, and it has many, many branches into other more specific areas, such as biomedical engineering, forensic medicine, pharmaceutical science and also many non-laboratory-centric stuff such as health policy, clinical epidemiology, public health and preventive medicine, biostatistics and a vast number of other areas. To get a devoted career in the biomedical science, you'll almost certainly need to have a form of HDR (higher degree by research), whether or not that is some specific Masters program or just a PhD.
As for medical scientists: "medical scientist" is a fairly general term. I've been working recently with clinical epidemiologists and you could certainly call them medical scientists - but I get the feeling you're using the term more in the sense of a pathologist or something along those lines. To be a pathologist, I believe you need a medical degree. If you'd like some more information about 'medical scientists', I suggest you have a good read of this:
http://www.jobguide.thegoodguides.com.au/occupation/Medical-Scientist.
Hope that helps!