If Mickey Mantle had retired after 1964, he'd be an even bigger legend.

baseball-reference.com has this cool feature under "Finders and Advanced Stats" then "Advanced Stats" for a player.  It has cumulative data by year and here it is for Mickey Mantle. Note 1964, Mantle's 14th season when he was still only 32 years old.

Mickey Mantle 1962 Baseball Guide and Record Book by J. G. Taylor Spink [Public domain], via Wikimedia Commons

https://www.baseball-reference.com/players/m/mantlmi01-bat.shtml

To view, click the link above and cruise down to:

Cumulative Batting

Year	Age	G	PA	AB	R	H	2B	3B	HR	RBI	SB	CS	BB	SO	BA	OBP	SLG	OPS	OPS+	TB	GDP	HBP
1951	19	96	386	341	61	91	11	5	13	65	8	7	43	74	.267	.349	.443	.792	117	151	3	0
1952	20	238	1012	890	155	262	48	12	36	152	12	8	118	185	.294	.377	.497	.874	145	442	8	0
1953	21	365	1552	1351	260	398	72	15	57	244	20	12	197	275	.295	.384	.497	.881	145	671	10	0
1954	22	511	2203	1894	389	561	89	27	84	346	25	14	299	382	.296	.391	.505	.896	149	956	13	0
1955	23	658	2841	2411	510	719	114	38	121	445	33	15	412	479	.298	.400	.528	.928	156	1272	17	3
1956	24	808	3493	2944	642	907	136	43	173	575	43	16	524	578	.308	.412	.560	.972	166	1648	21	5
1957	25	952	4116	3418	763	1080	164	49	207	669	59	19	670	653	.316	.427	.574	1.002	174	1963	26	5
1958	26	1102	4770	3937	890	1238	185	50	249	766	77	22	799	773	.314	.430	.577	1.006	176	2270	37	7
1959	27	1246	5410	4478	994	1392	208	54	280	841	98	25	892	899	.311	.425	.569	.994	173	2548	44	9
1960	28	1399	6054	5005	1113	1537	225	60	320	935	112	28	1003	1024	.307	.422	.568	.990	172	2842	55	10
1961	29	1552	6700	5519	1244	1700	241	66	374	1063	124	29	1129	1136	.308	.425	.579	1.004	175	3195	57	10
1962	30	1675	7202	5896	1340	1821	256	67	404	1152	133	29	1251	1214	.309	.429	.581	1.009	176	3423	61	11
1963	31	1740	7415	6068	1380	1875	264	67	419	1187	135	30	1291	1246	.309	.429	.582	1.011	177	3530	66	11
1964	32	1883	7982	6533	1472	2016	289	69	454	1298	141	33	1390	1348	.309	.429	.582	1.011	177	3805	75	11
1965	33	2005	8417	6894	1516	2108	301	70	473	1344	145	34	1463	1424	.306	.426	.576	1.002	175	3968	86	11
1966	34	2113	8810	7227	1556	2204	313	71	496	1400	146	35	1520	1500	.305	.425	.574	.998	175	4147	95	11
1967	35	2257	9363	7667	1619	2312	330	71	518	1455	147	36	1627	1613	.302	.423	.566	.988	173	4338	104	12
1968	36	2401	9910	8102	1676	2415	344	72	536	1509	153	38	1733	1710	.298	.421	.557	.977	172	4511	113	13

Provided by Baseball-Reference.com: View Original Table
Generated 7/26/2024.

In 1965-1968, Mantle's final seasons, neither Mantle nor the Yankees did much that was especially noteworthy. The Yankees did not even contend for a pennant.  Division play began in 1969, the year after Mantle retired.  Mantle would not have been tarnished with those losing teams after being on 12 pennant winners.  The demise of the Yankees would have been directly attributed to the absence of Mantle.

The only major milestone reached by Mantle was home run number 500 in 1967.  All things considered, The Mick would have been much better off by leaving while he was still at or near the top of the American League.  Mantle already had three MVP awards (1956, 1957, 1962) and three seconds (1960, 1961, 1964).

In 1964 Mantle broke his tie at 15 with Babe Ruth for career World Series home runs with a walk off winner in game three, then homered in games 6 and 7 with his team facing elimination in each game.  WS homer 18 was off Bob Gibson.  With the Yanks facing elimination in game 4 of the 1963 WS Mantle homered off Sandy Koufax in the 7th inning to tie the game 1-1.

Mick had 454 home runs through 1964, one more than Willie Mays in many fewer at bats (AB): Mays 7,036, Mantle 6,533.  In 1965 Mays hit 52 homers to zoom past Mantle.  In retirement, there would have been the speculation, no matter how unrealistic, that Mantle might have matched Mays.

For combined seasons, up to 1964, Playing in the AL or NL, in the regular season, requiring At Bats >= 0 and Home Runs >= 400, sorted by descending Home Runs.

https://stathead.com/tiny/8jgRV

Rk	Player	HR	AB	From	To	Age	G	PA	R	H	1B	2B	3B	RBI	BB	SO	BA	OBP	SLG	OPS	OPS+
1	Babe Ruth	714	8399	1914	1935	19-40	2503	10627	2174	2873	1517	506	136	2214	2062	1330	.342	.474	.690	1.164	206
2	Jimmie Foxx	534	8134	1925	1945	17-37	2317	9677	1751	2646	1529	458	125	1922	1452	1311	.325	.428	.609	1.038	163
3	Ted Williams	521	7706	1939	1960	20-41	2292	9792	1798	2654	1537	525	71	1839	2021	709	.344	.482	.634	1.116	191
4	Mel Ott	511	9456	1926	1947	17-38	2730	11347	1859	2876	1805	488	72	1860	1708	896	.304	.414	.533	.947	155
5	Lou Gehrig	493	8001	1923	1939	20-36	2164	9665	1888	2721	1531	534	163	1995	1508	790	.340	.447	.632	1.080	179
6	Stan Musial	475	10972	1941	1963	20-42	3026	12721	1949	3630	2253	725	177	1951	1599	696	.331	.417	.559	.976	159
7	Mickey Mantle	454	6533	1951	1964	19-32	1883	7982	1472	2016	1204	289	69	1298	1390	1348	.309	.429	.582	1.011	177
8	Willie Mays	453	7036	1951	1964	20-33	1848	8003	1379	2204	1282	354	115	1290	873	822	.313	.388	.589	.978	161
9	Eddie Mathews	445	7051	1952	1964	20-32	1933	8390	1303	1951	1146	294	66	1240	1240	1195	.277	.384	.526	.911	149
10	Duke Snider	407	7161	1947	1964	20-37	2143	8237	1259	2116	1266	358	85	1333	971	1237	.295	.380	.540	.919	140

Provided by Stathead.com: Found with Stathead. See Full Results.
Generated 7/26/2024.

Mantle's batting average would have remained well over .300: .309.  His OPS would have been over 1.000: 1.011.  Mantle's slugging average would have been higher than that of Joe DiMaggio (.582 to .579) and the length of their careers much closer: plate appearances: Mantle 7,979, DiMaggio 7,673.

Unfortunately, in 1964 Mantle passed Babe Ruth in career strike outs: 1,348 to 1,330. Mantle's SO total through 1968 was 1,710. That was passed in 1978 by Willie Stargell: 1,746. See "Progessive" leaders:

https://www.baseball-reference.com/leaders/SO_progress.shtml  

Updated 7/26/2024 to show cumulative stats for Mantle's entire career, not stopping at 1964.