Many years ago (2005-2007) I killed lots of people on Rookgaard (using slime) to get their apples. I still have about 30 of them on my rookstayer. Anyway, the question is actually quite interesting so for old times' sake, I decided to test it out.
1st test
Swearing to the king to have just 1 hp, then drinking slime:
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Nothing happens, slime doesn't work at all.
2nd test
Drink so much slime to die normally, from full hp to 0:
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@up
My hp dropped to 11, poison still works.
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Poisoned status stopped at 10hp. I drank another slime, but as you can see it didn't work.
Conclusion - nowadays it's not possible anymore to die by drinking slime.