Mr. Dalmia has given valuable advice. Kindly revert.
In case of sick leave employee should produce on his own medical certificate, and diagnostic reports, pathological reports, etc on his own and if demanded. This enables the employer to obtain in house opinion or from a specialist doctor to ascertain the adequacy of leave request. The employer can ask for opinion of super specialist doctor from institution or appointed by it.
The medical disorder mentioned by you is to be treated by a specialist doctor say a Gastroenterologist, Hepatologist and you might have been under treatment of an expert doctor or institution.
It is believed that you have produced all documents desired by the employer, and mentioned tangible and prudent reasons for being unable to attend domestic enquiry. External enquiry may mean examination by external team of doctors..
Grossly speaking termination during sick leave may prove to be a bad order.
Usually it is mentioned in appointment letter that contract can be terminated due to prolonged absence from duty (and some may mention due to sickness).
Valuable advice of learned experts/members is sought.