If Bonding Comes Off, Will the Etching of the Tooth Be Visible?

When you have enamel hypoplasia (poorly developed enamel, or poor quality enamel), it can lessen the strength of the bonding. The durability depends a lot on where on the tooth the bonding was done. In your case, on the front of the tooth is a fairly predictable place to bond. I wouldn't worry much about the bonding coming out-if it does, the tooth will look odd because of a divot from where the filling used to be. Not so much from the etching making it look bad.

If there is any trouble keeping the bonding on, then visit a cosmetic dentist. They are usually experts in making the bonding strong as well as getting a result that looks great.

Etching roughens the tooth surface microscopically. If the bonding comes off, the  tooth might have a slightly different color, but the main issue would be if tooth structure was removed in order to cover the yellow spot. If tooth was removed, then that area could be visible. I really wouldn't worry about this, even if it does come off, it sounds like a relatively small amount of bonding to replace.

If anything, the yellow spots that were on tooth will probably look a little lighter from the etching. If the bonding comes off, some of it will still probably remain on the tooth anyway.