Has Mentor Headlands re-opened after the flooding? If not yet, when is it expected to re-open? While there was a lot of news when it flooded a few days ago, nowhere can I find any news about it re-opening.

Yes

It will be flooded today with the amount of rain.

Its open there i believe you can call fairport coastgaurd or city hall of mentor

The west side is still slightly closed. The east side is accessible, just slight standing water.