Abandoning pipes in slab

I'm working on a house on slab with under-slab plumbing, all copper. In the attached garage there are supply lines (hot and cold) coming out of the slab near a side wall. This is original to the house, built early 50s.

The lines apparently were used at one time but not recently. Just 18" copper sticking out of the slab. They are functional. We are in cold climate and this garage was always heated. New owners would like to abandon these lines and stop heating the garage. Would you

1. Break the slab, cap them off under the slab and patch up the slab or
2. Break the slab, cap them off and put some sort of access box and cover or
3. Any other/better idea for keeping them from freezing while making them code compliant? Any way to avoid breaking the slab?

Just capping them even under some concrete will not prevent them from freezing. You have to find where they come from, cut them at that point and drain the water. If they are never to be used again, I'd chip out some concrete and cut them below the surface and patch the concrete. There would be no point in any kind of access to them unless he wants the option of using them some day. But if they are not drained, they will freeze and break.

pipes

If they are going to be abandoned, find where they come from and terminate them there. Then just cut the pipes at the floor and cement over them.

I see what you guys are saying. Not sure how true.

Obviously the soil under the house slab doesn't freeze (that's where all the pipes have been for some 50 years). The pipes in question here come out of the garage slab about 6 ft outside of the heated house. It may freeze there if the outside temp gets low enough. I don't know. I may have to drill the slab and stick a thermocouple in there to test for it.

Tracing the pipes is not real easy because of thick slab and lots of rebar.