[electronbeam]

1st stage reusability matters more so they can reach a cost model similar to F9, second stage is really just bonus.

If they never get the second stage working with reusability they could strip the design down to a simple S2

[jjk166]

If they struggle with first stage re-usability for a while, that merely adds cost. Further they probably want to iterate and scale anyways, so in the short term they're gonna be building a lot of first stages anyways.

Second stage reentry is necessary for this thing to ever carry people, ostensibly the mission the ship was designed for. It is a hard requirement.