The player lays waste to a sprawling horde of vermin and conquers the room! Then he leaves.
We all know not all DROD players are male. The game can't use the excuse that it's talking about Beethro, since this also happens in Negotiations. And sorry, Strunk & White, but practiced and accepted usage of English pronouns has changed over the years.
There are all sorts of creative replacements for the second sentence above:
That done, it's time to head elsewhere.
Oh yeah, and leaves the room, too.
(If anyone wants to suggest more, bear in mind that there might be significant puzzle between killing the last monster and getting out of the room, or it could just be a straight walk out.)