There is no such thing as a two-person ticket. You are definitely on two tickets, possibly under one PNR.
If your friend cancels or no shows, his ticket will be dealt with under its fare rules. Your will remain intact. The only exceptions to this are odd coupons where someone is sold a second ticket at a deeply discounted price. That is generally a credit card offer and handled through the CC and doesn't appear to be your situation at all.