There are many parts to EC261 and many people think it's just about compensation, when in reality the most value part is "Right to Care". Broadly speaking I would expect easyJet to give a same day alternative service, and if that is not possible (given they don't formally do connecting services) then they are on the hook for paying the replacement ticket.

But you can go on to BA's Avios area and simply buy replacement Avios, which is £125 for 6,000 Avios, so broadly £210 for that flight, which I would say is pretty good as a last minute purchase (if you had zero Avios it may be worth paying for Avios in this scenario).