You would need to provide more details for a fair assessment. What was the reason of the BA flight cancel? Was it weather? If not, what exactly was the cause? Was your friend on one single itinerary, or was he on two seperate tickets? What kind of ticket did your friend have? What level of "compensation" are you asking for? Is an alternative flight that will eventually deliver your friend to the final destination not enough? Are you asking for hotel bills and other expenses occured due to the delay? Or are you asking for money or miles as an apology?

No offense, but while BA may have done something wrong, we won't be able to say so unless we know what really happened.