My wife and I are booked to travel LHR-VIE.
2x C Avios redemptions, traveling out 7-12-12 and returning 9-12-12.
Also using a 241.

[Before anyone starts, the 241 was about to expire AND the job I'm doing in VIE is on an all-inclusive fee basis, so using Avios made sense]

Anyway, for various reasons my wife may not be able to come on the trip.
I will not know for sure until less than t-24 from departure.

Can anyone offer advice on:
a. if I can cancel her ticket so close to the booking yet still travel myself.
b. if I can change my return (assuming availability) closer than t-24 (I know that after departure I cannot change)
c. if I use the outward ticket then purchase a oneway VIE-LHR to return home on 8-12-12, will there be a problem with no-showing / cancelling for the scheduled return?

NB: the 241 will be lost in any event - even if it was reissued it will be valid until its original expiration of 10-12-12

Sorry this is so complicated!
Thanks in advance