from Germany it is difficult to assess the practice of Dublin deportation in France, In general I think the french authorities wouldn' consider Germany a "bad" county in which your medical treatment and therefore your lives are in danger. The medical treatment in Germany is on a good level and even asylum seekers normally get necessary measures if they have acute problems. In Germany asylum seekers or people with Duldung don't stay without housing (like for example in Italy), get food and minimum of help for their existence. The fact that you are rejected in Germany wouldn't normally influence the decision of France, as far as the asylum procedure in Germany isn't counted as disagreeing with the european guidelines.
In France you have a possibility to make an appeal in the court against Dublin decision, like in each EU-country. But the chance can be low. Anyway if french authorities don't deport you during special time, you can stay in France and make your asylum procedure there. Normally this time is 6 months after the agreement of Germany to take you back. In Germany if you make an appeal to the court, this 6 month time starts again after a rejection of the court. I have no idea if the court procedure in France also have influence.
If somebody in your family is so sick that this person can't be moved (for example is in a hospital), then it is possible that France doesn't deport you within 6 months even if the court doesn't stop it. Or sometimes the deportation just doesn't take place, nobody knows why.
But I have no idea about chances for Pakistani in an asylum procedure in France or about chances for humanitarian protection because of health problems.
If you come back to Germany, you can make subsequent application (Folgeantrag) but you need new reasons, for example new attests from doctors showing something bad which was not discussed in your previous asylum procedure.
For everything which relates to France it is important to find a good councelling center or a lawyer there. The same is important in Germany because it is not possible to discuss any detail online.