If they cut the Metaverse spending tomorrow, there's still a huge legacy ads business throwing off a ton of revenue. The company will do fine. It probably will not grow to Apple size.
Also note that from an accounting standpoint, the metaverse spend is not being treated and amortized as an investment. Instead, it's a cash expense. This means when Zuck decides he no longer needs to spend 10B+/year on it, that money will mostly drop right to the bottom line. The existing business is a cash volcano.