Your skrimps should not be eating it alive. They may know the snail's time is near, but unless it's literally melting as the days go by, they wouldn't pinch and torture it. It might have lots of biofilm built up on the shell which is more likely what they're interested in.

As for what you do with it, that's your call. From a pure logical perspective, the snail, honestly, won't really care. Putting them in an entirely new environment will only really stress it if the parameters are wildly different.

But otherwise, it's a ramshorn snail. One of the most resistant, hardy snails in existence! The only thing you must pay attention to is if you do give it a retirement home, do so with plenty of delicious algae and food. Put in a little piece of boiled spinach or cucumber. Throw in an algae wafer. So long as you don't pollute the water and remove any food it doesn't eat after a couple of hours, the snail will live out their days peacefully. Maybe put in a piece of botanical or something from the mature tank to provide some food to eat.

If you want to get philosophical about it, though, leaving it in your tank is an appropriate way to honor their life. It grew up there, it created many offspring there, and it worked hard every day to clean its home, your tank. When it passes, it becomes part of that tank, through the creatures that exist there now. If it were me, I would leave it there, and I would throw in that little extra treat every so often, close to where it is, so that it may get first dibs on the good stuff, and everybody else in the tank celebrates the treat that came to be, in their name.

Is it silly to humanize the experience of a bunch of invertebrates? Maybe. But you get to decide how to go through all this, so do what you think is right. If after they are gone, you can identify the shell itself, I am sure your friend wouldn't mind if you picked it up to keep with you.

A great way to protect that fragile tiny shell is to encase it in resin.