A lot depends on the roo. The hen can store sperm and lay fertile eggs for as much as 3 to 4 weeks, but there are variables; there is no "always" answer. The presence of a roo doesn't even guarantee any eggs will be fertile, in itself. If he's a good roo, not rough on them when mating, doesn't force the issue, etc., they will probably be fine. If you free range, he provides some protection. Some roos help manage hen squabbles. But if he mates with only a few, their feathers will probably get torn, and all your eggs may not be fertile. Some roos even cause cuts on the hens' backs. Sometimes hens seem more content with a roo in the flock, sometimes they seem more peaceful (and may even lay more) without one. Again, lots of factors to consider.