I don't think anyone knows for sure yet as no games have been patched. The system seems to do a lot with the SD card like background caching and some minor DLC so it may do patching. I would guess it's at least possible to do minor patching (some Wii games do it) but I don't know if it will become a major part of the system.
I just wish they'd patch Ghost Recon so it'd quit crashing on me. That game is so much fun but I don't ever play it because of the crashing.
I hear that affects a lot of people but honestly i have never come across this problem and i have played about 10 hours of it. I've had this problem also. It's very annoying to be pretty deep in a level and have it crash on you losing everything you've just done. Especially since some of the levels are fairly long. I've had it crash on me a couple of times right at the end of a battle. This was my favorite game from launch and I've put quite a few hours into it already but I do always have that fear that its going to crash on me.
I don't see that happening. Wii games, like XBox and Playstation games are disc based so all the game & save data is stored on the hard drive. The 3DS games are still cartridge based so all the data is saved on those carts as I believe the only rewritable data that can be altered is the game saves.