I am pretty young considering the average age of folks on this forum is probably 70, but i have been around lots and lots of silting in ponds and have come to this conclusion:

You will save yourself tons of money, time, heartache, frustration, and have a much better end product if you can drain out the pond, dig out the silt and start over again.

If that is not feasible at the moment, I would wait until it is.

If 8 feet deep is your deepest depth, your average depth might only be 4 feet deep? I wouldnt count on getting too much accomplished with a day and a half of the dragline. wont be a longterm solution.

I wouldnt rush into any decision, and the fish should not be a deciding factor to save unless they are all TROPHIES, which I dont think they are given the age and condition of the pond.