Re: How long does the save card last?
The DS Card? I'm not sure.
I have a game from 2007 - Digimon World Dawn - that I have restarted multiple times (at least over 10 times) and it stills works almost like new on my DS Lite, save a very very rare glitch (it's hit me 2-3 times now). The cards themselves last at least 5 years judging from this with good treatment, and can probably last much longer.
As for save files? No idea ^^'