return their investment to where.. maybe you should learn bitcoin. there is no central company called bitcoin.. thats the brilliant point of it. you never get your coin from a central company. its always a currency you get from people.

can you get a return of investment on your house without anyone buying your house??.. (answer is no)
(you can return your house to the bank. but no guarantee they will give you the full/any return on investment you put into the house when you default on the mortgage)

..
you do know what currency is right.. its a medium of exchange..
the purpose of currency is that it does change hands. meaning it is exchanged for something else of value deemed reasonable to the parties involved in the exchange.

if you want some 14 day return policy of 'if your not completely satisfied with your purchase then send it back to us and we will refund you' go buy something that has this extra customer satisfaction condition.
not all retailers give products a satisfaction returns policy. and that does not make the product a scam.
products do not come with satisfaction aftersales service as standard. its upto the seller to offer it. not the product

infact. i have sold BTC to people and a few days later they have changed their mind and i took their btc back and gave them their money back at the original purchase rate.. so to answer your question.. yes someone can return their investment without funds contributed by new investors..

you just have to find the right person to get the coins from that offers such a customer satisfaction returns policy..
retail products dont come with satisfaction returns policy as standard. its upto the retailer to decide if they want to offer such a complimentary aftersales services.