Here are the number of survivors (395) that I found just by looking through the Official Records and a few other sources:
226
Prisoners (Life of Forrest by Wyeth, pp.359-60)
The use of the OR on disc so you can word search is certainly a good way to conduct research, much better than a certain forum member ( pun intended) to copy paste wikki as your own work, without citation, and not know its bollocks.
Wyeth has much to say, including the demands for surrender or Forrest cannot be accountable for what may then happen, for several other forts he took/failed to take in the campaign. The relevant point here is that once you decline to surrender, you survive at discretion of the other side as you have absolved them their obligation from taking you as a pow. Wyeth aslo gives examples of Union Officers negotiating in bad faith, perfidy, during such negotiations, under the law this allows at the tactical level, summary execution as they are no longer a legal combatant with any rights.
CSA fought the war under the existing US Articles of war, in that there is nothing about not giving quarter to a soldier, ie its not an illegal act, those who surrender only to then fight in the same engagement are outside the protection of the law, Mil law only applies to members of the military, slaves in arms were subject to the states laws on slave insurrection, which basically meant summary execution, be it by burning at the stake as in NY or beheading etc.
Mil law does not define a massacre, it uses unlawful killing of 3 or more as a mass killing. Politicians and media use the descriptive term for dramatic effect. The intent to commit unlawful killing is not present at Pillow as the offer to surrender and be treated as pows was declined, and Forrest makes clear that absolves him from what may then occure, ( page 319 Wyeth) the blame rests with the Officer who made that choice, as it was a vote by all the officers they all share the responsibility.
30 at Memphis unwounded
"Of the 221 officers and men [6th US Heavy Artillery] who went from here, there are thirty here who escaped, and some twenty or more above at Mound City and Cairo." -Lt. Col. Thomas H. Harris, Memphis, TN, April 26, 1865 (US Congress Report No. 65, p.97)
89 wounded taken aboard the Platte Valley (April 13)
"The wounded I placed on board the Platte Valley for transportation to the New Madrid [Missouri] Hospital."
"We removed 69 wounded from the battlefield, besides 20 I took on board before the flag of truce was sent in by the enemy."
-Acting Master W. Ferguson, USN (OR Navies, Series 1, Volume 26, p.222)
20 wounded taken aboard the Red Rover (April 13)
"After the Platte Valley stood up the river with all the wounded found in the fort and around on the contested ground some 20 more came in from the rebel lines badly wounded. These were received by Fleet Surgeon Pinkney on board the Red Rover, which vessel fortunately came down the river at this time." -Acting Master W. Ferguson, USN (OR Navies, Series 1, Volume 26, p.222)
10 wounded taken aboard the Moose (April 14)
"...when Captain Fitch [USS Moose] returned from Fort Pillow he brought away with him refugees, women and children, who had been left there, and ten wounded soldiers who had been there for two days."
-Capt. A. M. Pennock, USN (US Congress Report No. 65, p.60)
20 deserted on the night of April 11
"...there were some twenty of the Tenn. Cav. deserted during the night of the 11th."
-Surgeon Charles Fitch, 13th Tennessee Cavalry (Personal Papers of Physicians, Record Group 94, National Archives)
Fitch is one of the more interesting ones in the OR, the full account is here and has a lot of relevant information example he has 69 as not yet mustered in, so they are not soldiers with any protection of the law, but are slaves in insurrection out of 700 total, ( compare to Wyeth page 31 total of 557) still a 50% casualty rate, so nothing oit of the ordinary in terms of casualties for an engagement.
https://www.tn.gov/content/dam/tn/environment/archaeology/documents/staffpubs/arch_Cimprich and Mianfort 1985.pdf
February, 1862, Major General Curtis issued a general order against CS guerrillas, US later Liber code exempted them from pow status, ie the could be summarily executed.
"persons guilty of such acts, when captured,
will not be treated as ordinary prisoners of war; they will not be shot but will suffer the ignominious punishment of being hung as felons."
1864 Custer executes by firing squad 4 of Mosbys men, and hangs 2 more, Mosby asks lee permission, which he gives to likewise execute 6 of custers officer held as pows. This tit for tat forced Lincoln to abandon his General Order No. 252 that CS pows would be executed in retaliation, as he found the CS was just as capable of meeting his bluff with more dead pows.
Several Union commanders, B Butler were termed "outlaw and common enemy of mankind" by the CSA, no protection of the law if taken, just execution for their war crimes.
This, excessive actions, is what happens when the government makes all the people the objectives of war.