echnically, YouTube will not “take” subscribers.
What is more likely to happen is a general cleanup of subscribers.
This is something YouTube does once every so often to filter out the fake from the real subscribers.
In the end, it will be actually beneficial if YouTube removes fake subscribers from your channel, as they do not add any value other than the subscriber numbers.
If your friend lost 200 subs, they are probably fake subscribers in the end.
As your friend probably already knows, it is better to build a subscriber base by creating high-engaging content.
As a sidenote, I would check to see where those fake subs are coming from. In most cases, fake subs have nothing to do with YouTube growth at all.
You want to build a community, not numbers, and even worse, they won’t give you the YouTube analytics data that you will be using to actually grow your YouTube channel.
Keep making awesome content and share it with the world!