What happens when a goal is reached
When approved supports reach the target, the goal is marked filled and the date is recorded.
On your page
The bar reads full and the goal is marked as done rather than disappearing. People who gave to it can still see the thing they were part of.
There is a share card for it, so you can post a picture of a filled goal to whatever you use. It is on the Share screen under Images.
On your dashboard
The goal card shows it as filled. The switch that takes a goal off your page goes away, because a finished goal is not something to pause.
What you should do
Post an update. That is the whole social contract of a goal: people put money in for a specific thing, and the last update is where they find out it happened.
Starting the next one
Add a new goal. On a free page, turn the old one off and the new one on, since one shows at a time. On Premium you can keep several and choose which one leads.
If money keeps arriving
It keeps arriving. Nothing stops, because nothing was ever being held. Supports above the target still count and still show, and the goal simply reads as more than full.