Originally Posted by schmare

Yes - skipping the LHR-CDG portion of a ticket will result in all subsequent segments being cancelled, so it's good you double checked!

In light of the new info you provided, I'd suggest calling the airline to find out what the cost would be to change your international ticket to arrive in Nice rather than Paris. It may not be possible (or it may be prohibitively expensive), but it also may be an option worth pursuing.

And your original plan of buying an easyjet ticket from Paris to Nice will, of couse, still work.