Without at least 6 sats, it can't tell where it is much less where home is, so RTH is impossible.
All it can do is fly in ATTI mode and drift with the wind.
Also note, home lock won't work either.
Land in place isn't a good idea either since it could be over a tree, water, or people.
The downside of not landing is that if the wind is blowing fast, the Phantom will fly away fast leaving you little time to realize it's no longer holding position before it drifts out of range.
Another reason to keep it within LoS so you can fly it manually if you have to.
I practice flying in ATTI mode sometimes just so I can do it efficiently when needed.