personally, I'm a bit of a worry wart, and wouldnt fully trust anyone to tear into it- I'd ask to be there when opened up to take a peek on my own- specifically looking for any shavings near the drainback holes(in case a cam bearing might have spun in the head, or roller lifter might have locked up) looking at the cam lobes(even bumping over to see all the peaks, in case a lifter roller failed and started wearing in), if anything 'bad' might have happened some scoring/discoloration/metal filings ought to show up somewhere inside. If its just a sticky hydraulic adjuster, everything ought to still look minty shiny with only 7k on it.
My worry would be they dont want to fix the same problem twice, and might just throw the easiest parts at it first- say a roller lifter locked and cut into the cam a bit- replacing it might let it run fine for years- but the worn lobe might not ever fully open that valve again. then if it continues to wear under warranty, they can replace the cam next time...
Personally the other thing I'd opt for is if ONE lifter is bad, only replace it. Even rolling parts will 'seat in' and replacing all of them would just restart unnecessary break in wear again on a bunch of parts that are already as good as they will get. I've pulled ticky lifters from old motors and taken them apart to ungunk the little metering parts/pistons inside rather than simply dropping in a new cheap lifter- more work, yes, but a new one wont 'match' the cam and would rather not risk wiping a lobe...true not much risk with roller cam lifters, but still...
anyway, hope they get you fixed up quickly.