What happens when a game is a draw?

For example, I won the first round with 42:38, then I lost the second with 22:30 and the third round ends in 5:5.

All I was able to find was that the Nilfgaardian Empire will win any round that ends in a draw.

Besides that, will the game take previous rounds into consideration, is there a sudden death, or is the game simply a draw?
Also, how are the rewards distributed in case it really is a draw, and there is no winner?

According to this Reddit thread, when 2 non-Nilfgaardian players draw, you can choose to instantly rematch without consequence:

What if it's the third round? Does the game officially end in a draw?

Yes. You can instantly have a rematch without consequences.

This is further confirmed by the same thread stating that this is even the case in tournaments:

Even tourney games that end with draw can be repeated

This other Reddit thread also seems to confirm this:

In a regular draw you get a chance to replay.

This thread from the official Gwent forums claims with respect to awards:

The only strange thing is, if your whole match ends in a tie it counts as a win-win on endscreen, but doesn't give any rewards to anyone.

So to summarize:

A tie is considered a win for both players, but there are no rewards provided. You are also given the opportunity to play an entirely new match against the same opponent.