How long will they last? That totally depends on their tricks, their marketing and people awareness.
Although I think they will last a little longer than other ponzi schemes because:

1. they are cleverly making users feel that they are investing in 'bitconnect' coin, which is not the case.
2. they are offering low ROI as compared to many other ponzi schemes.
   If your motto is to grab some profit, you can try with small amount. If you are lucky enough to reap good profits before the company run away, good for you.But this may be hard, as there are a lot of negative reviews for this program on google, and people will obviously do research before investing in these kind of schemes. :P
   In my opinion, it would be better to mine that coin instead of investing in such ponzi scheme. ;)