You would get 50 points from this flight towards your status so you would have 305 points; don't reset it unless you don't plan on earning GO. Assuming you really mean 50 points each, you would get another 50 points for the second flight so your new total would be 355 points.

The balance part of your account, will just show 0 points required to renew; only the total will show overflow.

For example, this is my account page, as you can see the left side shows how many points earned for my current tier, and the right side shows how many points I need to renew (and in this case it's zero since I already earned enough for renewal):