I am a plumber, and have also done plumbing work for American Home Shield, which is a home warranty company. They will never cover anything "outside" the foundation of your home. It will be in the contract and even if you put on your gorilla suit, like the other guy said, they will not waiver on anything outside the foundation of your home, sorry.
That being said, did u have the slab leak from day one or did it present itself a few days later onward? Your realtor MAY be able to get some recompense, but I doubt it. Slab leaks are easy to repair, just very time consuming to get to to make the repair that's why it's usually expensive, the labour involved to repair. The concrete is probably the cheapest part of the repair, and if it was outside, you probably don't have much damage, so the home warranty is skating free. I assume, like California, a home warranty comes with your first year of purchase of a home automatically, I wouldn't renew afterwards. When I was a home warranty tech, I was told to put "band-aids" on as much as I could and try to deny as much as I could, not by the home warranty co., but by the plumbing company I worked for contracted by the home warranty. That's why I left, I thought it wasn't fair to the consumer, I just don't have a head to rip people off, especially for the betterment of someone else.
Since the leak is outside, I would call a plumber and see that if that line is going somewhere you don't even really need since it's outside maybe it's going to a hose-bibb you no longer need or a sprinkler valve you could do without and he/she can isolate it and say goodbye to the line itself. Otherwise, it appears u may have to tear up the patio and repair it or otherwise get the line re-routed. Either way expensive. Good luck.
By the way, also check and see if you have high water pressure. That could have caused the slab leak to begin with. A lot of times high pressure will do that. It should be 50-70 psi definitely no more than 80 psi. You can check it yourself. Assuming you have a regular tank water heater, go to a hardware store, get a pressure gauge for about 5-10 bucks. Go to your water heater, where the water drains out and screw the gauge on there nicely and open the drain on the water heater, if it is a newer water heater, u may need a flat-head screw driver to open it. And check your gauge. You can even leave the gauge on there permanently to check out your pressure. No worries it wont leak unless you've crossed threaded it. Check it the next day for leaks. Here's a couple of things:
1. Accurate pressure relies on NOTHING being opened in the house, not even a toilet running. U will get an inaccurate reading. Of course, since you have a slab leak, unless you isolate (shut-off) that line, you will have to wait for the repair to check the sysem pressure.
2. If you do remove the gauge from the drain of the water heater dont forget to CLOSE the valve up first, or u will get scalded.
3. You can check the pressure at a hose-bibb instead, but unless you are absolutely certain that the bibb is AFTER the pressure regulator, I always check at the water heater because I know it's a regulated system.
4. In older homes, you may not even have a pressure regulator, in that case install one if your pressure is high.
5. As a matter of usual inspection, the water pressure should have been checked by the home inspector, PLEASE don't take this for granted, as a plumber I always run into new home owners where the inspector has listed the pressure as normal and I have found sometimes 180 psi, some inspectors just won't do their jobs right and unfortunately, you sign off on any kind of liability with them.
6. In rare cases, you may have a thermal expansion problem, that is, that when you have the gauge on the water heater and you turn it up (the temp) all the way and if that psi climbs significantly, then you have thermal expansion and not so smart plumber will only check a static line to see the pressure. Have the plumber check it at the heater with the burner going full blast if you have thermal expansion, it can easily be rememdied with a thermal expansion tank by the heater.
Lastly, if your water heater is old, over 10 years, I wouldn't mess with the drain, it might not close back up correctly because the rubber seals have been set in a certain way for so long, when you disturb the rubber, it has no pliability to seal back up, so check at the cold side of the bibb thaty serves the washing machine. That's another great place. Or if the drain on the heater is plastic, be very careful, if that plastic is old and u try to screw a gauge on too tight, the drain will crack and u may get scalded and create water damage. Good Luck. I am at firstname.lastname@example.org if u have any further questions.