As far as I know, with 2nd layer technologies, you can pretty much have lower denominations than a satoshi. So there's that. It's going to be very likely that pretty much everyone is going to use 2nd layer technologies for daily transactions anyway(in the future, that is), while using the main-chain for larger settlement transfers.
Not sure we need to worry about this yet.
A bit too early that's for sure. There are smart people working on Bitcoin. Whatever problems arise, potential solutions will come.
I agree with you, most likely to use the technology of the 2nd layer, if certainly not come up with something else