I'm not *entirely* sure how it works; Jon and Stephen are both guild members, so they're not supposed to be writing. I know they've been improvising to some degree, and TDS has aired a few correspondent pieces that were ready before the strike. Parts of the shows certainly do still seem scripted - I'm not sure who's doing that or exactly to what degree it's planned in advance, though.
But the talks apparently went really well this week! Hopefully it'll be over soon ...