What would you do?

Due to a lack of rain and a crack in the irrigation pipes, my pond as receded quite a bit. Inside the pond was a plastic "flap" that was held on by a chain that could help release the water through the pvc. On the other end, a large brass spigot had cracked and has been slowly leaking water since last winter.

Water freezing in the end of the pipe will ultimately cause the spigot to crack but I am unsure how to recreate what was done by the original owner. I am tempted to just close up the pipe and not allow it to be drained unless someone was to swim under water and unscrew the cap, which I know won't be me

Any input that could help me here? I live in Maine and am moments away from the water freezing and/or snow ending this project until the spring.

If the pipe is not needed to regulate water height then I'd make it go away. By regulate, I mean if you have a flood and the pipe is not there, is there a spillway or something in place to let the excess water leave? If it has nothing to do with that function, no need for it.

The pond has never overflowed, and I believe the original intent to having the pipe there was for draining to periodically clean the pond and to provide possible irrigation to animals. When the pond is high enough, there is a small overflow on the south side of the pond.

If the overflow area on the south side of your pond that you mention does not provide a compromise in your pond wall, and it has a place to drain away from the pond in a way that does not cause erosion to your pond wall structure, then it acts as a spillway. If the spillway has the potential to remove all the excess of a massive unpredictable rainstorm event when the pond is already full, then you've got no worries, otherwise, I would expand the spillway and rim it with rocks, such that it can deal with whatever storm comes your way.

It seems like if you already have a pipe running through the dam you might as well make use of it. I would put a proper PVC elbow on that pipe (don't glue it!), add a riser that would be just above the level of the full pond, and set up a Holzer style "Monk" that could be used to take water out of the pond to the level that you want (to do this you would tilt the pipe off to the side to let water in, and drain that amount of water out). Fix the gate valve and make sure you drain all the water out of the pipe from now on before winter hits. Do a forum search on "Monk" and you should be able to find detailed instructions on how to build this. It should be pretty easy since the pipe is already there. You've got the water there you might as well keep your options open to be able to use it in as many ways as you can!

I think this is the thread where they talk about the "monk", how to make and use it:
https://permies.com/t/1360/ponds/Sepp-Holzer-ponds-monk