Power demand would have to drop significantly for that idea to work. I don’t think semiconductors are even capable of delivering enough computation with only 2 mW. Maybe a completely different sort of technology could pull it off, but currently there’s nothing like that in the horizon, so who knows if we’ll ever get human powered devices. Maybe some tiny computers with hardly any processing power could be a realistic application.
If you merely abandon your account, the change can be seen in the MAU statistics. If you delete it instead, you’ll make sure you won’t slip in the future. Either way, investors care about the active users, because the total number of accounts isn’t a very useful number to them.