If he was smart it'd be to a very limited extent.

If you have this much wealth in something as unpredictable as the stock market I think the very wise move is to start converting it into stock backed loans[1] that you leverage to buy real assets - buy islands and small countries, buy other successful large companies and just let them keep trending slowly upwards, pick up that New Zealand bunker... just try and get your money diversified and into things that would survive a stock price collapse. Even if Elon did this with 1% or 10% of his wealth and kept the vast majority of his assets invested in this one clump of companies and they went to zero he'd still be sitting on an insane pile of cash.

1. Lets all pour out a drink to the bankers who authorize such insane loan agreements.