Do you have any evidence/comments saying someone killed him without the Willsapper dropping?

The "Rarity" tag doesn't necessarily reflect the % chance of dropping. You'll notice Vaniki's Heart has a "level to attain" of "55" versus the "60" for Willsapper. Part of Willsapper being "very rare" is the wacky spawn time of Vaniki and desirability of it.
http://everquest.allakhazam.com/db/item.html?item=3949
http://everquest.allakhazam.com/db/item.html?item=22809


July 2001 Comment on Zam
Magelo lists a drop rate of 100% for both items. (Granted the entry date on the modern site is 2011)
http://eq.magelo.com/npc/420232

I have been unable to find any evidence to indicate anything short of him dropping the Willsapper 100% of the time.

Also, reading through the two pages on Allakhazam, there are many posts detailing every little bit of the fight and what he does including the Willsapper procs, the couple spells he repeatedly tries to cast on you, his amount of hitpoints, when he gates, how hard he hits, how many hitpoints he has, etc... It's curious to me that only two posts reference the supposed 500 DD, only one of those two posts was what I would consider a detailed accounting of the encounter. Nonetheless, of the many, many posts detailing the encounter, most comment on how incredibly easy he is, and I find it nearly impossible that so many obviously detail-oriented posters would neglect the fact, or simply not notice, that HE JUST SO HAPPENS TO HAVE A 400 DAMAGE-PER-SECOND PROC.

Not sure if that's really sufficient "proof" that he's supposed to have that proc, and just because it's detailed in that EQMac parse from 2011 doesn't mean it was implemented during the original Velious timeline as there were many things on EQMac that weren't "classic."

If the "Rarity" category has no correlation to drop rate for items; then I retract my Willsapper drop rate adjustment proposal and apologize. I have no additional reference material at this time concerning that detail.

The detailed EQMac parse corroborates the in-era posts confirming a 500 point proc.

Spin this as much as you'd like but it is a classic mechanic.

EQClerics August 2001

But Nilbog already made this classic so all is right in the verse.

So the only evidence for this change is an incorrect era parse from EQmac, and an in era post that incorrectly identifies the proc as a life tap? Neither of those sources independently provides accurate information, and I don't really think it takes much spin to at least raise questions about their accuracy together.

And 2 posts on Allakhazam about a 500 point DD proc.

And I'm sure more information could be found. But Nilbog understands that EQMac is the most classic source of information in recent memory and it jives with three independent posts all identifying it as a frequently cast/proc'd 500 point direct damage spell.