This is my opinion on what happend to Namepopper. Keep in mind, for the most part, it's educated guessing and I may be wrong.
As you may know, many domainers like to keep their personal information somewhat secretive. Just try asking those in forum chats if you can call them to talk on the phone, many will make up an excuse as to why you can't call.
Very early in the game, it's likely someone asked NP for his name (perhaps old boss GregR), rather than give real name he said nickmaster, i.e. "web master" as in Inter-Nic etc. However that person thought he meant Mr. Nick Master, so the name stuck and it also became his Mod Name. It is extremely unlikely Nick Master was his real name, in all likelihhood was a non-de-plume.
It also is believed he wanted to avoid personal contact with domainers (other than thru PM's and posts) as he always refused various efforts at personal contacts and apparenty never once spoke to anyone on the phone. Than is actually far from unusual as many domainers are like that, not just NP, for various reasons.
NP quickly became the
#1 Moderator at DNF, and perhaps the best Mod in the world. After zillions of hrs and many PM's on the forums he likely started to get burned-out, as anyone would. He was thought to be more active (plus helpful & appreciated) than all the other Mod's at all the other domain forums combined, also more popular than others.
Then GregR sold DNF to DotComGold. It appears very likely from reading posts (reading between the lines) and pm's, NP did not really like DCG and the way he proceeded to so heavily commercialize dnf and some other things about new management, including the occasional deletions of some posts, and not too much communications vs the old ownership, especially soon after the sale.
NP was getting even more burned out over all of that and also having to suddenly make more defensive posts and pm's too, and even more often.
It also appears NP may have been personally upset that he was not offered an ownership interest in DNF or at least some monetary compensation for all his time and effort. NP likely became very bitter about that, thinking he contributed more to DNF success than anyone (which he likely did), but could not share in its success.
Finally, NP also realized most of his domains were unfortunately not good and really had basically zero value. I personally looked at several dozen of NP's domains and did not see any with even reg fee value. Sometimes he did have some real good ones (like Flowers.org or GIF.org) but he sold them too quickly, for believed to be somewhat low prices. Sorry to say, except for a few notable exceptions most all of NP's domains were worthless, but he probably did not fully realize this until late in the game
If you combine all of the above one can easily see why he would let his names expire, disappear, and totally drop out of the business, especially if those rumors of poor health also were correct. This is all only an opinion and I could easily be wrong about some or all of this, but think this is the most likely scenario.