It really is impossible to say, for good commercial reasons this is unknowable. If the aircraft isn't so busy that definitely helps on one level, there again I've seen Avios seats available on overbooked services too. There is no firm rule here, and nothing you can do about it other than checking online every UK morning time to see if there are any updates (doing a dummy redemption rather than pressing the UUA button), then call up as soon as you can thereafter if something shows up. I wouldn't take the seat map apparently being empty as a sign of a half-loaded aircraft, plus TLV is notorious for late bookings.