A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,413
This assumes that the ticket wasn't booked as two for one or some similar deal.
If you're concerned, you can always split the PNR first (at any time) and then cancel one ticket according to the fare rules (or for free within the 24 hour period).
Remember that PNRs can never be combined, so don't book separately initially.