McCoy was the chief medical officer on the Enterprise in the 1st season TOS (and not in the TOS pilote episode) and joined the Enterprise 2265. In the 6th movie McCoy answered in the Klingon court-room, that he served as ship's surgeon and chief medical officer for 27 years. Therefore the "Khitomer peace conference" was hold 2294 or 2295.

Captain Montgomery Scott is rescued by the USS Enterprise-D from the crashed USS Jenolen trapped with an alien Dyson Sphere artifact, after being suspended in the transporter for ca. 75 years. (6th season TNG: Relics).

That happened 2369. Going back 75 years we get a date between 2291 and 2296.

But the crash of the Jenolen must have been after the conference of Kithomer and after the end of Star Trek VI.

That is why we can say for sure:

• Khitomer and Star Trek VI happend 2295.
• The Jenolen crashed in the same year of the Kithomer conference or at least one year later 2296.

Afer Mr. Scott rematerialized and he had heard the name Enterprise, he asked about Jim Kirk. Therefore Kirk was still alive in the time of the Jenolen-Incident.