The company valuation should really correlate with the revenue performance and the daily active players in the games they own. All the licensed IP is worth quite a bit also. The digital assets they own will always be fluctuating but the actual business (gaming) will just keep growing. Mine craft is still going strong and look at Roblox. If we are just to refer to sandbox alone, this is early days. Give it at least another 12-24 months after the game launches and we will be able to see exactly how popular it becomes. If it hits a million active daily users then the valuation is more than justified already from just one game and one IP IMO.
By all means I am not advising anyone to hold. If want to sell then by all means please do so. Plenty of profits on the table. But imo this will list in the foreseeable future at high multiples to what it is now.