So "you can't restore bass once you roll it off" isn't quite right — you might as well argue that rolling off bass is necessary because you can't restore treble that isn't recorded.
Maybe I am misinterpreting this, but I don't think it is really accurate. Bass roll-off doesn't have any effect on higher frequencies, at least not in absolute terms, whereas it definitely reduces the low frequency content (both absolutely and relatively). Depending on the corner and slope, you could lose some low frequency content to an extent that EQ'ing it back in would be difficult/impossible (particularly when coupled with proximity effects from directional microphones or with microphones that don't have good low frequency response to begin with).
For the OP, given the sensitivity of those mics, you can probably go either mic-in (on low) or line-in for most shows. According to the specs, there is an 8 dBu difference at the "default input level" (whatever that may be), so there is probably a pretty big overlap between the two. If it is really loud, go line, and if it is really quiet, go mic...