I know when a phone is powered down it will go straight to voicemail when someone calls. Is this the same for when a battery dies, or is there a chance that it can still ring through before voicemail picks up?

I ask because a friend of mine is missing, can't get ahold of him and given the circumstances of when I last seen him I worry something bad may have happened rather than just him being avoidant, but I'm not sure. The thing is when anyone calls it will ring the usual 4 or 5 times then voicemail picks up. It's been almost a week since I've heard anything, I would assume that if something bad happened the phone battery would've died at this point, if that's the case would it automatically go to voicemail or is there a chance that even with a dead battery it will ring first before voicemail picks up?

Unfortunately I don't know what phone he has, never really paid that much attention but I know his service is through US Cellular.

Any help appreciated, thanks!