John Heilemann expects big things:
[I]f Romney comes up short, Ryan almost certainly will still have a big future in the GOP. As I and others have noted, there is going to be an epic struggle for the soul of the Republican Party if Obama is reelected, with recriminations aplenty regarding Romney's failure to bring home an eminently winnable election. But no one is going to blame Ryan for that, and he will surely come through the storm with an enhanced reputation among the Randian faction of the party, not to mention nearly 100 percent national name recognition, and the invaluable experience of having played the game on the national stage. Assuming that he runs for president in 2016 — a statement akin to "assuming Heilemann quaffs a bourbon in the next six hours" — Ryan is all but guaranteed a top-tier position in the Republican nomination sweepstakes.
A Romney loss on Tuesday most likely spells the end of any presidential ambitions Ryan may have had.
That doesn’t mean that Ryan’s career has to be limited to the House. The good news for him is that an increasingly likely Thompson loss creates an opening for a future Senate bid later in the decade. If Thompson were to win, Ryan’s options in Wisconsin politics would be very limited, and it is probably the case that Ryan won’t be a national contender in his own right until he is able to contest and win a statewide Wisconsin race. It’s one thing for partisans to enthuse over a House member as VP nominee in the middle of an election, and quite another to back him as a presidential candidate.