Repair-It

Of these. But I don't know what it's called. My deck is coming down soon, because Vinyl siding is going up this week/next week.

And I don't want anyone walking out into midair. I can find plenty of railing sections on Home Depot's website...

Like this:
http://www.homedepot.com/p/DeckoRail-Pr ... /203879870

But can I just bolt that to the house?

I guess I'd want that lagged into a 2x4, not just the plywood sheeting. There is probably a code regulation on that. Aside from the code, I think it would be safer. If the 2x4s didn't line up, I'd build something after the siding is removed to land where I wanted to bolt the railing.

Maybe I could lag 4x4s into the door framing (assuming spacing is correct, and use these, which are intended to bolt into Newell posts..
http://www.homedepot.com/p/DeckoRail-Pr ... /204606980

That could work.

Maybe I should just keep the deck...

Replace all the railings, etc...

I'd probably do what you're doing for budget reasons knowing you could always revisit the deck situation later on after this sting heals. You can put a deck on a sided house with no problem. Just a little flashing work to deal with. It's not like you'll pay twice the price to do the deck later or something.