@ ninnicab – 07/09/2015 02:29 BST
If you go back to the OP, you will see this topic done to death.
If you don’t take the flight from CDG-LHR (or from wherever), then your ticket will be annulled. You are also strongly advised to complete the entire itinerary on the return because there is also a risk that non-completion will lead to BA recalculating the fare basis and demanding an additional sum to pay. Beyond that, try using ITA Matrix software to find out where the cheapest ex-EU jump-off point is. AMS often scores well and, for fares to the USA, both DUB and OSL appear to come out well.