This crossed my mind because Ayato and Laito's routes in Dark Fate explored a concept of trying to forgive and let go of Cordelia which they were able to do with the help of Yui. I for a while believed that because they were able to move on from Cordelia that they would be able to move on from Yui if her was placed into somebody else. I don't believe that anymore because even though Cordelia didn't have her heart in Dark Fate Richter was still loyal and simping for Cordelia. He's always like "I will do anything for my beloved Cordelia!" with or without the heart and so I think the diaboys would still only have feelings for Yui. I think that if a demon sucks enough of Yui/Cordelia's blood or if the holder of the heart spends enough time with a demon then they fall in love for real and can't let the person go even if the heart is moved. Edit: After their feelings awaken they can't let the holder of the heart go even if they no longer have that heart.
Another reason they would still have feelings is because the guys were still attached to Yui in Lunatic Parade even without her heart and Shu, Kanato, Carla, and Shin even discussed turning her into a demon which means she would have a different heart (examples are Kanato chapter 1 and 2, Shin's ending in Lunatic Parade). Subaru at the end of track 4 of his Daylight CD said that he wouldn't let Yui go even if her blood wasn't special and that her blood doesn't mean anything to him anymore. I believe him! Subaru in track 5 of his Daylight cd said that her blood would taste special regardless of its taste as long as it's "her blood" and he wasn't talking about the heart but her herself. He would sacrifice everything for Yui (the other vampires too) the same way Richter would sacrifice anything for Cordelia (except Cordelia doesn't seem to have feelings for Richter and Yui of course has feelings for Subaru lol). I think that the Daylight CD's and Lunatic Parade routes in general do a good job showing that they are not just attached to her because of her special blood. When their feelings are awakened they can never let them go.
