Inground pool leak damage question

We have vinyl-liner-type inground pool. The bottom and the walls of the pool are concrete.
This year, while opening the pool, I discovered that the white plastic flange of one of the water return jets had cracked into pieces and fallen into the pool, leaving only the protuding mounting screws and a rubber gasket which is now loose. I've also noticed that the water level is slowly going down over time, suggesting that water is now leaking through that outlet opening.
I spoke with my pool dealer (the installer) about this and during the conversation, I asked if they thought the leaking water would be going out to the ground. They stated that it probably would be leaking down UNDERNEATH the liner. When I asked if that would cause a problem, their response was "You want to get this fixed as soon as possible."
I'm concerned about this because this is a fairly large pool, the water level has dropped a good 6 inches (i.e. that's a LOT of water) and they seemed to suggest it would be ending up between the liner and the pool walls/floor.
If the water is indeed accumulating underneath the liner, will that cause problems? Would it be trapped there forever (i.e. until the liner gets replaced)?
Thanks for any advice...

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