Can the bitcoin lightning network support more than 8 decimal places? Say Bitcoin goes to 1 a million dollars. We need more decimals, but btc core only supports 8 decimals? By that time its safe to assume everyone will be using lightning to do transactions, but will lightning have support for more than 8 decimals?
Lightning uses millisatoshis as the unit of account for all transactions and routing fees, but the sub-satoshi balances are not reflected on the bitcoin blockchain in the event of channel closure. 

When a channel is closed, any sub-satoshi amount held by each party is dropped from the commitment/closing transaction and goes towards payment of the on-chain transaction fee which miners collect.

Amounts below a satoshi, or rather, below dust_limit_satoshis, are made cooperatively between the parties of a channel and are not enforcible on-chain, but if many of such transactions are made, they add up to whole satoshi amounts which will be enforcible in later commitments.