There are many debates all over the internet in terms of the death of Mirza Ghulam Ahmad. However, after double checking many sources, its obvious that the earliest Ahmadiyya newspapers and books totally avoided the “cause of death” for MGA. It should be noted that MGA’s enemies/critics, i.e. Sanaullah and Dr. Khan’s comments on the “cause of death” for MGA are all missing. However, in 1915, Farquhar wrote that MGA died of cholera, however, he gives no source at all. It wasn’t until 1927, and the autobiography of his life wherein he mentioned that MGA seemed to have died of cholera.  
_____________________________________________________________________________________________The Vakil
The Al-Hakam, via

“As his condition became precarious, we stayed by him and continued treatment, but his pulse stopped by 10:15 A.M., on the 26th May, 1908 he breathed his last.”

(Al-Hakam, May 28, 1908)
_____________________________________________________________________________________________Other ahmadiyya newspapers

The english version of the Review of Religions didn’t give a “cause of death”, however, the Al-Badr, Urdu-Review of Religions, Tashishazul-Adhan and other newspapers are unchecked.
_____________________________________________________________________________________________Muhammad Ali in 1917
Muhammad Ali writes as follows:

“he suddenly fell ill at about 10 o’clock on the evening of the 25th May and expired at about the same hour on the morning of the 26th, in the house of Dr. Syed Muhammad Hussain Shah, in the Ahmadiyya buildings. The body was carried back, the same evening, to Qadian where he was buried on the 27th of May…” (see page 52).  
_____________________________________________________________________________________________Mahmud Ahmad in 1915

Mahmud Ahmad wrote about the death of MGA in 1915, however, that edition of the book is missing, it was most likely edited. This is the 1998 edition and it seems that this was book was missing from the records for 60 years, since it was published in 1967.