Sick pay after 78 weeks (Knowledge of health insurance)

As far as I know, the health insurer decides on a case-by-case basis - so ask your insurer!

If you get sick for an extended period in Germany, you get your normal salary for 6 weeks from your employer.
Then, if you are still employed and member of the public health insurance scheme (private insurers might differ), you get a smaller payment (apporox. 70% of your previous salary) as Krankengeld from your insurer for another up to 72 weeks (making it 78 weeks of paid illness) within three years.
After that, you might get Berufsunfaehigkeitsrente (disability pension) or social security, if you are eligible.

Thank you very much for your kindly reply, beppi.  Before I go to my insurer, I'd like to ask you one more question.

But first of all, here is my case.
1) Yes. I am still employed.
2) Yes. My doctor keeps giving me sick notes.
3) Now it's the 71st week.
4) I cannot go back to my work not because I'm handicapped.
It's because
a) I cannot keeping sitting, standing or walking for over 2 hours. I need to keep changing my posture; otherwise, my back pain will come back. (Herniated disk problem)
b) Lifting anything at work can simply hurt me badly.
5) I refuse to have a surgery what my colleague did because my health conditions are getting better and better (but of course very slowly) And I believe one day I can completely get well, have my normal life back and go back to work again.

Now the question is :
In my case, which of the benefits at this moment I am able to have (most likely),  Berufsunfaehigkeitsrente, Arbeitslosengeld, or...???

I'm sorry to ask so many questions.
But it is essential for me to know my situation first and I can prepare some terms and wordings in German before I talk to my insurer, because the colleagues of my insurer I speak with are not really willing to speak English.

Thank you very much 

You can only get Berufsunfähigkeitsrente (disability benefits) or social security (Hartz IV) when your entitlement for Krankengeld is over (and the three years period for Krankengeld are not over yet). You should approach your Berufsunfähigkeitsversicherung, Rentenversicherung or Jobcenter for this.

Krankengeld is limited to 72 weeks within a three year period. What You alluded to above is another 72 weeks in the next three year period, which, if I understand correctly, starts approx. 1.5 years from now in your case.
You also cannot get Arbeitslosengeld (unemployment benefits) because you cannot work - and you are not unemployed.