You can find all the relevant information at Wizz Discount Club Terms and Conditions.
As you can see from there:
1.10... The club member must remain a passenger in the booking at all time for the other passengers to beneficiate from the club fares. If
the club member is removed from the booking, the regular fare will be
applicable to all remaining passengers and the fare difference will
need to be paid. Alternatively, one of the other passengers can become a
club member to keep club benefits for the remaining passengers.
So, don't worry, your friend can still use the flight if you are still on the booking (not necessarily traveling).
However, if you will remove yourself from the booking (which is unlikely), then your friend has to pay the fare difference, which is most of the times 10 € for the flight + 5 € for the baggage. However, if the difference is larger than 30 €, your friend can become a club member himself for 29.99 €, as was suggested above.