He has it already.
It's in his character writeup in the Rogue's Gallery.
"Possessions: Headband of Vast Intelligence +6, orange prism ioun stone, tome of clear thought +5 (read at level 20), 21,000 gp black onyx gems, 101,000 gp diamond dust, 20,000 gp incense (gate component), magic jar focus, scrying focus, 2 true seeing ointments, 2 symbol of death components, spell component pouch, shapechange crown,
blessed book (symbol of death cast on it, triggers when touched), cloak of resistance +5, scarab of protection (12 charges remain), ring of protection +5,
ring of spell turning, handy haversack, greater rod of quicken, greater rod of empowerment, greater rod of maximize, sustaining spoon, contingency focus, 346275 gp
Staff of Malacarus: 10 charges, contains the following spells: greater teleport (1 charge), plane shift(1 charge), greater planar binding(1 charge), mass suggestion(1 charge).
Custom crafted, widely recognized and feared. Price: 63,000 (bought at full market price to represent crafting a while ago)"
It's reasonable to assume the Gate component is spent to call the Balor.
I also think it's reasonable to assume that he wasn't carrying the full 346,275gp on his person when he died...that much cash, he'd probably have most of it squirreled away, and only a smaller "spending wallet" on his person. Specifics are between Mal and the GM, of course.