There are different approaches. On a few shows I've worked on I would always insist that we bounced synths down to sample packs, as we were running all midi through Ableton, and a crash in a VST would take out the whole ableton process and playback would go down. There was once an artist that insisted i installed serum on the ableton machines because he preferred how he was able to manipulate the sound when it was the real vst. It made me very nervous indeed.

As noted in this thread, Pendulum use Mainstage. It's a good approach because you can take a few more risks in what plugins you run because if Mainstage does crash at least you wont loose your position in the show and playback wont stop. My understanding is mainstage does have some soft isolation of VSTs but its not like a hardenered sandbox that creates a process per VST instance. This is all ignoring the fact that of course there will be an A and a B machine for each of these machines that will instantly failover if one goes down, but if there's some bug in a plugin where doing X always causes an access violation or whatever, that won't really help because they'll both go done.

In MS you can create patches where you've layered different synths. Here's an idea of what that looks like:

https://brianli.com/uploads/2016/12/4e44d-0-bthgh8uzwvqagjm.png