I'm actually against Donut's view as I want to make all the PC-98 cast (and Rin) popular. I think they deserve more attention. I just have this kind of urge to make barely noticable/non-existent/forgotten people popular and loved. I would probably say Mima and Shinki, just because I know nothing about the others. Without meme's and ZUN's characterization, they barely "exist". And I don't like that.
Also, ZUN said that these characters won't be out of place, rather he can't think up ideas how he should bring them back, like because if they're back, people would like to ask them "where have you been?" and that's a nuisance, especially for all those characters. And ZUN likes to think up new characters instead of bringing them back.
So I just stay at my Expanded Universe view: PC-98 characters exist, they never left, just they weren't in the games. I mean, it's not like everyone in this world is always on TV, right?