What is the deal with these?  I've noticed a bunch have opened up recently, many of which conveniently offer a single "Investigation Agency" located abroad to handle removal cases for a 500$ fee.  Has anyone ever used these or knows anything about them?  

Do these sites stay up awhile?  Or get shut down

they collect a fee to remove your data...  which they may or may not do...

how many ppl actually pay up?  do these sites just die on there own?

If you pay them $500 to remove you from a website, what is to stop them from listing your number again on a different website that they are controlling, and then extorting money from you again?  It is not like there is honor among thieves.  These blackmailers are also overseas, out of reach of the law, and you can't exactly sue them for fraud.  Don't ever pay them anything.  If you are listed on one of their websites, then change your phone number, and take it as a learning experience to use a 2nd pre-paid cell phone in the future.    

Do these sites tend to stay up awhile or do they go away eventually?

Web hosting for a cheap website costs $4 a month.  If they make a single $500 sale, that would cover their web hosting expenses for the next 10 years. There appears to be no incentive for these blackmailers to ever go away.  

Aside from that, if your phone number comes up in google searches and it goes to a website like that, the phone number will now and forever have that association as far as the search engine is concerned.  Anything that a search engine has ever indexed gets permanently archived somewhere.  That is why they say that nothing ever gets deleted off the internet.  Look at the way back machine website, it can show you websites that don't even exist anymore.  

Nigeria, India, Pakistan...  good luck serving them!