If Khan draws at least 10 000 (which he would) at an average of $100 US per ticket, that is $1 million. If Khan had no TV deal, and the fight is a one off PPV in England, I'm guessing it would still do at the very least 50 000 buys at $30 US per buy. That comes to a gross of $2.5 million before deductions for the cable provider.
You are looking at a worst case scenario of $2 million net, not including any revenue from the USA. This is revenue generated strictly from England.