Home many times the dome will stay hermetic until the needle finally make a hole that not closing ?
Hundreds, even with some abuse. The insertion point is far less of an issue than skin thinning, as mentioned by xMrB.
it’s reasonable to assume their is a one way or check valve in the filling system.
Nope, no check valve on the several sets I had had use of.
Relying on essentially a silicone bulb that’s been punctured multiple times is asking for trouble.
Not really. It is a medical device, expensive, and designed to take a needle through the port. Many, many times. Subcutaneous insertion points are common and uncomplicated for more banal and useful purposes like diabetes or dialysis, no?