Most Helpful Guy
He might, he might not. It would depend on a lot of things. How attached he was to the girl in the first place, what the illness was, and how the behaviour changes when medicated and when not. Whether or not it would be something that would be manageable over time, how long term he is thinking. How much he likes the girl in general.
If he is saying "I will consider it, IF I'm single, and IF you're all better", then that's not a positive sign. That's kind of just admitting he is not going to wait for the girl, he doesn't much care about her progress, but if he is lonely and/or horny and she is not a threat, then he may consider throwing her a bone. That's kind of shitty, and not very empathetic.
Getting help for mental illness is great, it's a positive and the girl should be doing it. But she should be doing it for HER, not for a guy. That's just putting the responsibility for her emotional well-being in the hands of another, which is almost always a terrible, terrible idea. She needs to get better for herself, so she can be the person she is supposed to be, and find a guy that will have empathy and understanding and acceptance of her condition and be willing to actually stick around should there be a relapse or additional complications.