One-ways from AMS to LHR in December start from £50 on KLM (of course, not every date will have this price), but you also have the option of maybe booking on BA.

Given that you are looking at saving the company as much as £1200, I would definitely advise getting your company to simply buy you a new one-way on any airline that suits you. This would mean you completely forfeit your current KLM LHR-AMS-LHR.

Your current ticket is probably not at all flexible, so you would probably only get the taxes back, less a fee, if you cancel (But maybe your company would make good your "loss" here, given that you are still saving them a substantial amount?). If you hold on to your ticket until closer to departure, and if the disruption at Schiphol (or even at Heathrow!) persists, there is a very good chance that you will be impacted by a flight cancellation and/or a schedule change, which you could then use to obtain a full refund, so it might be better to "give up" completely on your KLM ticket, but not cancel it yet in the hopes of still getting a full refund in the months ahead.

However, if you then book a separate ticket on the same return AMS-LHR flight as the rest of your group, for which you at that time already hold a booking (via your LHR-AMS-LHR ticket), then you might run into trouble if and when the system notices that you are double-booked on that flight...so it may be safer not to immediately book your "real" AMS-LHR flight on the same KL flight as your buddies.

Enjoy both trips!