I myself am excited for the Dawnguard Dlc but I do not have Xbox live so do you guys see any chance of Dawnguard going to a exspansion disk like Knights of the Nine and Shivering Isles in Oblivion?

Possibly there's a GOTY disk in the future. I wouldn't expect it until after the DLC's are done though.

It will be along time before they put it on disk, until Bethesda finish all the DLC they wanna release for Skyrim.
That is when there gonna put it on disk, which will be the Game of the Year Skyrim.

Confirmed not on a disk. Wait until it comes out on GOTY or get Xbox live.

It would be nice. If Bethesda is going to allow people to purchase Dawnguard at retail and not just digitally there are two likely scenarios
1. It will be on a download card or on your receipt at purchase, similar to add-ons like The Arrival for Mass Effect 2
2. It will come on a disk, similar to the disc for GOTY edition of Oblivion
Sadly, I think its more likely that you won't see Dawnguard in disc form as of yet because Bethesda plans to put Dawnguard on a disc with the next DLC, whatever it may be. Its not much difference, unless you want to install Dawnguard on a family member or friends account.
Edit: Confirmed that it won't be in disc form, sorry for the correction

Does Xbox Live silver membership allow Xbox Marketplace? If it does, you should be able to get it.

Yes. Xbox Live silver grants you access into the marketplace. So if he took his Xbox over to a friends who has internet, he would have to go through the process of typing in a code and other things to get the internet to work on his Xbox. How ever, that is unless he has once already allowed it to except internet from that person before. But do be aware their have been quite a few up dates and also that dashboard update. So your Xbox will have to be updated to allow you to go to marketplace.

It does, he shouldn't have a problem to download it unless there is no way to buy msp officially in his country, or if his xbox is jailbroken.

I wouldn't count on a Day One disc release, but I would assure you that most likely there will either be a Game of the Year edition with all the DLC once they're done making them, or they might release an install disc like they did for Shivering Isles at some point. Maybe around the time the PS3/PC players get it?

Here's hoping you don't have to wait for GOTY or Ultimate Edition (as they did with FO:NV) to play Dawnguard, though.

That said, if they DO release a Day One install disc, I will probably go that route instead of DLC (even though I have Live) because Tribunal, Bloodmoon and Shivering all included cool physical maps of the new areas.

EDIT: To those saying Silver lets you buy DLC, he may mean he has no access to Live at all. As in, no way to get his Xbox hooked to the internet, or has a router that doesn't agree with his Xbox hardware. That can happen, too. Although, OP, they are right, if you can get online. After all, why would Microsoft prevent you from paying them for stuff just because you're not a Gold subscriber? That would be silly.

EDIT 2: Just thought, OP, if you have a friend that has a way to get your Xbox online, you can take it to them, sign up for a Live Silver account (it's free) and buy it, then transfer your Skyrim saves to the new profile so you don't lose progress. Don't buy it on someone else's box, though, and put it on USB. The licenses won't work offline on a different Xbox than the one it was downloaded on.