Not really sure how to respond here...
firstly, I think if our bases were attacked and wiped out, we would counterattack and possibly start up the draft before they got to the invading bit.
Unless you're talking all-out war, and in that case I would expect a nuclear attack, in which case your second bit is mostly moot - we wouldn't have much in the way of people to draft, unless the antimissile systems I've read about are far better in their current states (read: still classified) than I think.
Then there's the issue of a government which got us into that level of **** through incompetence probably facing internal revolution, albeit possibly non-violent (as in, we impeach the worthless ****s and get some better talent involved).
So many possible scenarios, interdependent on various factors that you didn't cover.
In short, I got no idea.