Most voice actors are eager to return to projects. They won't do it for free (and nor should they). For the most part, voice actors don't turn down roles. Sure, they'll tell the fans they love the role and they would love to get more work voicing that role. And maybe some of them do make connections with the media (as we do; they're human, too) but it's also always a job. A gig. The next paycheck.
It's less common (and far more noteworthy) when voice talent will not return to a role. Usually because of somebody involved. Rarely due to the ethics of the subject matter — again, it's just a gig. It's just acting. Acting a role does not endorse things done by the role. I mean, nobody who voiced or portrayed Hitler in films was an actual Nazi with six million kills to his name. People act roles of unethical people all the time. And sadly some fans take it personally — like the way Lena Headey (Cersei) and Jack Gleeson (Joffrey) were treated after their roles on Game of Thrones (both good voice actors and, AFAICT, decent people who loved the source material and wanted you to hate their character because it would get you emotionally invested... but neither actor deserved any of the real-life hate (including death threats!) they got). Even so, people who play villains are almost always as willing to return (if their villain character wasn't killed off) as people who play heroes.
I remember hearing that they wanted to re-record their lines for the Legendary Edition (remasters of the Shepard Trilogy). Of course they did. It's more paying work.
Definitely go meet these people at conventions if you can. I haven't met these two, but a lot of voice actors are theater nerds, and theater nerds are fun as hell. Probably the most fun people you can meet, especially if you can find common ground. One hit me up because he liked my phone case. I wasn't a fan of anyone he voiced, but my wife was, so she was sitting there drooling (not literally) while he and I were talking about phones and old computers. He invited us to hang out with him throughout the weekend, and of course we went to his panels and stopped by his table when he was doing autographs, just to say hey. Another one threw together an impromptu scene from a popular Shakespeare play and invited fans to try acting for a few minutes. And as my wife and I had already met him, he picked us first. She wouldn't do it, but I did. Never had so much fun at a convention. (I'm being vague because I don't want to call anyone out, even for good deeds. Meet the ones you like. Most of them are awesome.)