Server 2012 R2 Standard with Essentials Role - How to properly License for true "Essentials" Experience?

We have a customer that bought a server and bought Server 2012 Essentials R2, sat on the hardware for a year and never deployed. Over that year, they grew from under 25 users to around 40 and now they want to deploy the server they bought last year. Believe it or not, they are an office of 40 and still have no server.

So, we are likely going to buy back Essentials from them, not install it ...and instead install Server 2012 R2 Standard with 40 CALS and deploy the Essentials Role, since they like the features of Essentials.

They plan on occasionally using Remote Desktop through the Remote Web Access site. Does that mean we also need to sell them 40 RDS CALs? Or does Server 2012  w/Essentials Role only require RDS CALs if you plan on virtualizing desktops?