Most stuff that i read only mentions that he either preserved the city and stopped any efforts of destroying it or he ordered a ransack for 3 days, but not the fate of the civillians (except for that one book by Roger Crawley, where he mentions that all civillians got enslaved)
From before dawn to the early afternoon on 29th May 1453, the Turks entered the Constantinople and to kill, pillage and enslave. The Greek biographer of Mehmed II, Michael Kritovoulos, writing less than a decade after the Fall of Constantinopole, wrote:
Then a great slaughter occurred of those who happened to be there; some of them were on the streets [...], others were in their own homes and fell victims to the violence of the Janissaries and other soldiers [...], still others were fleeing to the churches and making supplication - men, women, children, everyone, for there was no quarter given.
He goes on to report the numbers who suffered in the siege and sack:
There died [...], men, women, and children, well-nigh four thousand, and a little than fifty thousand were taken prisoners...
Kritovoulos spends several pages talking about the suffering of the people, 'honourable old men', 'consecrated virgins' and 'tender children' all enduring terrible ordeals at the hands of the victorious army. Of course Kritovoulos had an intention in mind - he wanted to place the magnitude of this siege in comparison with those of Rome, Carthage, Jerusalem and Troy in order to make the subject of his biography, Mehmed II, seem as important as possible. Kritovoulos directly compares the Fall of Constantinople with these cities. Looking at other sources further communicates the brutality of the sack. Leonard of Chios, a Genoese defender who escaped, claims that 60,000 were enslaved and reports the 'foul debaucheries' suffered by the women and youths. It must be remembered, however, that the writer of this source left the city as it was falling so cannot have known for certain the details he reports.
Another source, which slightly differs, is Doukas, a diplomat who entered the city in the days after the sack and spoke to Janissaries. Doukas reports:
[The soldiers fleeing from the defences] on reaching their homes and finding their wives and children already abducted, were themselves bound and fettered with their closest friends and their wives. The old men and women who were unable to leave their houses [...], were slaughtered mercilessly. The newborn infants were flung into the squares.
This last account shows that the sack of the city was of course brutal and merciless yet was not as indiscriminate as other sources would suggest. The emphasis here appeared to be on capturing valuable slaves rather killing all who could be found. The fate of enslavement rather death seems to be what most of Constantinople's citizens met following the breaching of the city's defences.