It's worth enquiring. There's a good chance they'll fold rather than go through the hassle of having you complain.
That said, some firms assume they can boss the customer around, leaving them naught but the option of taking them to court to try and get the customer service the company's website promises but the arrogant twat of a customer service monkey refuses to deliver...
. . Sorry, got a little side-tracked there.
As I say, it does no harm to ask. You could even try the angle that the 16GB Sansa plus the 4GB card give you the 20GB player you're replacing
Well, if you 'decide' in the future that you do need lossless, it probably is just a placebo effect - I mean, your hearing's unlikely to get
better...
Still, as you say, you can't use it if it isn't there.
As for problems, well no DAP's perfect.
My Nano has frozen, just the once, though it sorted itself a few moments later. And I know people with iPods who have worked perfectly and others who have had quite a few problems - with either player you get, you run the risk of it being temperamental.
On that note, could you use part of the remaining credit to purchase some sort of plan for the Sansa like you did your H320? It wouldn't really be a separate item, so they might be a little more lenient.