I just tried it out, and Vemonus's answer is partially wrong, although their quote about what the developer said seems right.
Here's what I did:
- I went to the "Entrance" room of "Bergen Trail", then I noted my experience amount (about 701/1000 (I was level 13 at that time)).
- I started a combat rank: I killed a single mob (a bunny in this case, which gave me +22 experience).
- I walked to the "Rising Path 1" room of "Bergen Trail" and came back right after (to the "Entrance" room), so that the game knew I changed room, but left the combat ranked mode active.
- I let a mob kill me (still in combat rank, so I would expect to lose any progress).
However, when I respawned, my experience amount was higher (it had changed to 723/1000 (which is my initial experience amount +22)): There was no penalty.
In other words, when you die, you come back exactly to the first place you've been at in the current room, with the experience amount and the items you had at that moment.
So that's a little bit awkward because you can actually exploit this glitch to partially save progress while in combat rank...