Well, do bear in mind that the fates of Ratotskr's and Nidhogg's eyes differ. Niddy's eyes are used intact, but Ratotskr's eyes were actually eaten by Thordan and his knights. Whether even this is enough to truly kill a dragon is unclear, but if Ratotskr could be brought back, none of the first brood dragons seem to believe so. Both Hraesvalgr and Nidhogg seem to believe that she's dead for good. Midgardsormr hasn't said anything one way or another on the topic, and he'd probably know best.
At any rate, I think it unlikely that Ratotskr will be making any kind of return, though it'd be an interesting plot twist if it turned out that all people of Ishgard could band together to summon her, or something.
On the topic of dragon asexual reproduction, it makes me curious as to why dragons even HAVE genders. Is there any biological difference between a male dragon and a female dragon? Do they refer to each other by gender, or is that purely a human convenience to avoid using the less-than-polite "it" and "its"?