Do you remember what this character was fighting? It's usually the biggest giveaway, since novels are centered around specific conflicts.
The only thing I can think of involving a guy stranded in the desert is the Ciaphas Cain novel Death or Glory. He is en route to Perlia when the Orks attack his ship in the Warp, and he gets stranded with his aide on Perlia. He then has to lead a ragtag militia to safety.
Here's a synopsis:
Then again, Cain novels are distinct from other 40k
novels because they are not grimdark. Rather, they are picaresque, a genre centered around the adventures of an appealing scoundrel or thief-like character that allows the reader to explore the setting from the perspective of a commoner with a realist tone.