It very much depends on how the seller has set a reserve. If the reserve is discretionary, the auctioneer will do everything they can to sell the lot provided the high bid is at least vaguely close to the reserve. If the reserve is fixed, the lot will go down as not sold if the reserve price hasn't been reached but it's not at all uncommon for the auctioneer to contact the seller post-auction to conclude the sale at the high bid if that's close enough to the reserve.