You may putt with the flagstick left in the hole.
Plain-language guide · Rule 13.2. Use the current official text and your round’s Local Rules for a ruling.
What to know
There is no penalty merely because the ball hits it. Decide before the stroke and follow the rules for an attended or removed flagstick.
On the course
Tell your group your preference. Do not deliberately position the flagstick to help stop or redirect the ball.