That's a fair enough question. I have just looked through the easyJet website and alas cannot find an explicit statement that confirms it, but I have also scanned through their Terms & Conditions and - unlike other, legacy airlines - there is nothing in there that states a return flight is forfeited if the outbound flight is not flown.

Also, the video on this easyJet FAQ page clearly refers to "one way pricing".

The other thing to say is that lots of people have done just what the OP has done (missing the outward but flying the return) with no problems, unlike what can happen on other (legacy) airlines where the whole of the rest of itinerary can be forfeited if you miss a flight.

If anyone wants cast iron confirmation, by all means contact easyJet - their customer service offering is quite good.