You should never, ever wake a sleepwalker.
It’s not recommended to wake a sleepwalker because it’s a scary experience – but they won’t die if you do it. Since they’re in such a deep state of REM sleep, it may send them into a state of sleep inertia for about 30 minutes. So, instead of waking them up, gently guide them back to bed. They’ll thank you for it in the morning.