Praise be to Allah.
It is not permissible for you to take the salary in the two
cases mentioned, so long as you did not get a leave of absence that would
make it permissible for you to take the salary even though you did not do
the work (sick leave, if you were actually ill, or maternity leave, if the
system allows the pregnant woman to take a leave with pay).
In the first case, you should give in charity the salary that
you got, or donate it to public facilities that the state usually spends on,
and the closer it is to the field of your work (medicine and hospitals), the
better, because there was no one who took your place at work and you cannot
give the money back to the state.
In the second case, it also seems that you should give it in
charity, because the one who did your work in your stead did not do it in an
official capacity with permission from the one who is entitled to give
permission for that, and the employment system does not allow an employee to
appoint someone else to act in his stead, with or without a salary.
For more information, please see the answer to question no.
For information on things that prevent supplication (du‘aa’)
being answered, please see the answers to questions no.
And Allah knows best.