They *should* retreat, but they won't. This makes for a good final battle to conclude the series. After all, it'd be boring if they only ever engaged in low risk-battles.

There's three important events to happen:

- Defeating Death Spots to avenge Maryīs team mates
- Ranta proving himself to Haru
- Ranta finally summoning that demon he has been going on about every since episode 1

They showed us several stun-spells this episode. I think those will come in handy to focus on the smaller enemies while keeping Death Spot in place.
If I got to choose, it'd be awesome if Ranta fights Death Spots all by himself, proving that there are situations where you gotta have 1-on-1 skills.