It really depends on a few factors, did you book the reward flight which was then cancelled by VS? If so the rebooking policy has been developed over the summer and in most cases if no G fares are available then they will open up revenue seats and book you in irrespective of season and destination as long as it’s the same number of miles for the route and the same taxes. Posters on here have had mixed results with regards to contacting VS to achieve this, I have 3 G fares ( booked during the 50% off sale) and have 100% success with rebooking using the online rebooking form ( all my flights were cancelled by VS ) others have found calling or WhatsApp have worked and some have had no joy at all.
If you cancelled and took the open ticket option you will be subject to normal reward fare T&C’s, there will need to be reward availability, in the same season and destination etc.
My success story on this:
I had open tickets (2 x one ways) as a result of VS cancelling the previouly booked flights.
Both were reward flights (G's) booked in the 1/2 price mileage sale
I tried the online rebooking form. No response by text or Whats App .
I called VS...just under 2 hours hold.
Gave my 2 booking numbers and my required new dates for both flights.
Lovely agent said "no rewards available, hang on"
5 minutes later she had created both my requested flights to rewards, seat numbers sorted and new itinerary avalable online.
I didnt have to beg for them, nor argue about any price/points uplift. Nothing more to pay.
So I'm off to South Africa for the first time since December 2019.
Such great efficiency and impressive considering the pressure the reservations team are under.
I hope that if any one is in the same situation, you get a similar, positive result.