I suppose in this case it's probably a negative sum game. The assets in question are the FTT token that Alameda mined and gave to FTX as collateral, in return for real customer assets from FTX that Alameda used to gamb... er trade with. But FTT then went to zero, tanked the whole market, and the customer assets Alameda holds lost value too. Everybody loses.

At this point it wouldn't surprise me if they siphoned off the money by being on the other side of those trades via different entities...

Supposedly from what I'm hearing from /r/buttcoin rumors, Alameda was very bad at trading, so the billions have gone to the people doing the opposite trades from Alameda, which were being funded by FTX to try to gamble back the amounts lost.