Family Visit - Change of circumstances

I came here with my wife on 5 October 2015 on a family visit sponsored by my Brother-in-Law with a plan to return to India in December 2015. I have a six months visa valid till 18 March 2016.

On my arrival, the lady at the immigration desk checked my details and after asking the usual questions, pointed out to me the fact that I had come to the UK in September 2014 and stayed here for 5 months (I had a valid six months visa), and then after a gap of about 7 months, I have come back again, and this time I should not attempt to remain for more than about 4 months or else I may face rejection problems in my next visa application.

But unfortunately after my arrival in the UK, my Brother-in-Law fell seriously ill and expired on 22 Nov 2015. This unexpected and sad turn of events has compelled us to remain behind for a few more weeks as we need to support the grieving family.

Do I need to inform UKBA about my stay extension, even though it is within the validity of my current visa? Though I am aware that I can legally stay here till my visa expiry date, but I am concerned about the warning from the lady at the airport immigration desk. She has not made any note in my passport or visa, it seemed to be a verbal warning from her.

Any advice will be highly appreciated. Thanks