You are fine IF you got all the plugs out and none were stopped up with silt or corrosion. If all the water is out, there is nothing to freeze. But if you missed a plug or if no water ran out due to a clogged hole,could be a problem . When we winterize, if no water runs out we always run a rod or coathanger or whatever in the hole to make sure it's not clogged. Sometimes exhaust manifolds don't ftain water so we always check. Biggest problem is missing a drain plug,happens every year to a few guys that do their own winterizing.