Ebay and Paypal both are very famous and they have customers in Billions so i don't think that it will go down soon.
Aslong as the internet keeps existing Ebay and PayPal will too, unless 70,000 people a day are going some other place then they are not getting smaller.
Apart from a scandal, there is no way ebay and paypal are going down the drain. Paypal is always the number one choice for online payment with big companies, and eBay is simply the biggest online auction host int he world by way too far to have that gap closed. Wellt hats what it think at least