But they are shown winning and getting the trophy
They do, but it seems implied that they won in death with the whole being exploded and thrown across the track at terminal velocity.
One could go with the cartoony themes that they didn't but the aura around them looks ghostly.
I never got that implication. At its core, it's a very simplistic racing anime. The cars did all types of funky stuff that violated physics. When related to all the explosions in the rest of the movie; the ending explosion is just par for the course. How did they survive that gigantic explosion from the satellite bombardment? You kinda have to suspend disbelief for the physics. This is not Evangelion with weird deep alternate philosophical interpretations. I found the anime pretty straightforward.