Ice Maker dead leg

I’m planning to connect my ice maker to my reverse osmosis filter, which will likely involve drilling a PEX line into the basement & running over to the fridge, back up through the floor.

As a result the existing copper line to the fridge will become a dead leg, six feet long or more.

I believe I need to fix this, but I keep wondering if there’s a good reversible fix. I would hate to just chop it all out permanently. Could I splice in a ball valve? Or would the small dead leg to the ball valve still be too big?

If there is no reversible fix, is a cut-and-cap advisable? A plug? Or should I go all the way and try to desolder the branch out of the T-junction?

Lastly, since this is cold water, just confirming legionella is still a concern? Our groundwater gets darn cold in the winter (Zone 5), but in the summer ambient temperature is within legionella growth range.