You have to keep an earring or something or else it will close
No, it can close up if you don't keep something in it.
Why do you have a fishing line in your tongue piercing in the first place
Yes
Without the jewelry to keep the piercing open, a cheek piercing will generally close within a few weeks. It can even happen in a few days if the piercing has not been there for a long period of time.
Put in a captive bead ring.
When it comes down to it a piercing is a hole.. Your body treats this as a wound that needs to heal.. Everyone's body is different as to how long the piercing will need to stay in before you can take it out without it healing over. There is no guarantee that your piercing will stay open without jewellery in it, The only sure way to keep it open is to leave jewellery in or if you don't want it to be noticed as much put a clear piece of jewellery in it. (a retainer) using anything other than this may be likely to cause an infection.
She can still keep her navel piercing in.
You can put a nose ring but it may be too small. depends on your nose. Nose bones or screws wouldn't show but they'd keep the piercing open in a pinch.
You could get a longer piercing but that could be uncomfortable and is not reccomended. Depending on how long you have had the piercing, if you have had for a long period of time the depression could take a very long time to disappear or could say like that forever if you decide to remove it.
If you're talking about the jewelry then forever if treated right, if your're talking about the hole then you have to keep it in for 6-8 months to let the hole stay not closed, My piercer told me that and I have a Monroe piercing and I'm getting spiderbites tomorrow.
Best not to mess with it your self, go see your piercer and for a small fee they can open the piercing using an insertion taper which will stretch the piercing without damaging it.
It depends on how big you want the hole to be. In some African countries they use a plug the size of a saucer to open the piercing.