No offense, but that is wishful thinking at its finest because you don't want Nadal to win the title. Nadal, a 12 times RG champion and winner of the last 3 RG in a row, will be the absolute favorite for the RG title with or without Thiem in the SF. Djokovic, with only 1 RG title, who has never defeated Nadal in a RG final or semifinal, is not going to suddenly become the favorite just because Nadal has Thiem in the SF.
Nadal won't get tired just for playing one 5 sets match against Thiem (assuming the semifinal goes to 5 sets rather than 4 or 3). I guarantee you that Thiem being in Nadal's half means nothing for the final. Djokovic has no realistic chance to defeat Nadal in a RG final, just like Rafa has no realistic chance to defeat Djokovic in an AO final. If Djokovic had to beat in 5 sets Thiem in the AO SF, he would still defeat a fresh Nadal in the AO final. Analogously, even if Nadal plays a 5 sets SF with Thiem, he will still defeat Djokovic in the RG final.