As you can see from this chart, originally it was normally singular like...
The full OED lists this usage as...
the like(s) of (rarely to): such a person or thing as; now often depreciatory. colloq.
Those two observations seem to confirm my gut feel that if you encounter like rather than likes in such contexts, it's much more likely to be an approving reference (because the implication of OED's now often depreciatory is that it wasn't originally so).
When I read OP's example my first thought was that I'd probably have written the like of Muhammad Ali. But having just compared hits in Google Books for the like of Churchill (4430) and the likes of Churchill (51,200) against the like of Hitler (16,500) and the likes of Hitler (70,500) I'm no longer quite so sure. Obviously almost all the first pair will be positive, and almost all the second pair will be negative. But proportionately, Hitler gets the singular far more often than Churchill, which is the opposite of what I'd expect.
Note that the construction in We shall not see his like again is almost always positive (and rarely involves the plural). Also note that I've used the relatively formal shall not rather than colloquial won't there, to reflect the fact that his like/likes is a bit dated/poetic.
But with no further context I'd understand We won't see the like/likes of him again as "disapproving" regardless of plurality (speaker thinks they're well shut of his sort / people like him).