Switching VST's

Now that more and more people are experimenting with using different sample sets, how does Dorico deal with it if someone with a non-Halion VST sends a file to someone who doesn’t own that sample set? Does the receiver have to set up the player manually?

Yes, that’s basically it. In the fullness of time we’ll have Playback Templates where you’ll be able to set up the score for your preferred instruments, but for now there’s just the default HALion template or the manual setup.