Scarring and just like any open wound, infection. A properly done piercing by a professional can not cause an infection (everything is sterile) and as long as proper aftercare is followed they heal easily.
2-3 months
No way to tell. Depends oh how old it is and how your body heals.
give it about a week or so it will be okay
1 year, the piercing takes a long time to heal if you want to take it out for good any time is fine. but if it's just to change jewellery about 6 weeks would be fine.
No way to tell. It depends on your body really. I wouldn't risk it though. I would get a clear glass or acrylic retainer. 9 months isn't very long for a surface piercing to heal.
a week at most
When you get pregnant, most care providers recommend removing your belly button ring. Even women who don't remove their rings report that belly button rings itch and pull as the belly stretches around the fifth or sixth month. There is also the risk of infection if the belly button ring scratches you or opens a small wound. If you do take out your belly button ring, the piercing hole will probably close, requiring you to re-pierce your belly button after having your baby. However, if you don't want to take out your belly button ring you may want to purchase a non-metal pregnancy piercing ring. These are flexible and two inches long to accommodate your growing belly. Pregnant women claim that this product allows them to keep their bellies pierced without the discomfort of other belly button piercing.
Its supposed to take about 6 to 9 months to heal but if you get pierced at a time where you have to sit alot it usually does not heal right and you'll most likely end up taking it out. I suggest getting it during the summer and clean it well and it should be fine in 6 to 8 weeks.
It is always best to wait 3 months in between letting your piercing heal and getting it re-done. Re-piercing too early can make your chances for scarring higher, and also raise your chance for infection if the previous one was not allowed to heal. Wait 3 months.
Your ear takes 6 weeks to heal from a piercing.
After 3 years chances are good it wont close, the piercing will shrink but not close completely.