"But God will redeem my soul from the power of Sheol, for he will receive me" (49:15). What did the psalmist expect?

The psalm says what the verse says, and no more. Receive me is one Hebrew word, yiqqacheni, from laqach, which Brown-Driver-Briggs gives as "take" (tap receive). The psalm itself uses the verb for the plainest taking: "for when he dies he will carry nothing away" (49:17). Scripture uses it too where God takes someone: "Enoch walked with God, and he was not found, for God took him" (Genesis 5:24). And another psalm has the verb with me: "You will guide me with your counsel, and afterward receive me to glory" (Psalm 73:24). Being brought up from Sheol can also mean being kept alive: "LORD, you have brought up my soul from Sheol. You have kept me alive, that I should not go down to the pit" (Psalm 30:3). Psalm 49 doesn't say which it means, or when. What it does say is set against the rich: they are "appointed as a flock for Sheol" (49:14), and "He shall go to the generation of his fathers. They shall never see the light" (49:19). Psalm 16's notes look at Sheol and corruption (Psalm 16:10), and Job 19's set out two readings of when Job expects to see God (Job 19:26); these notes don't repeat them, and don't choose.