I can play my monser full turn now, but Monique hit and kill OB4 (even if she didnt count -2 for the concealment).
Be careful with that line of thought Psi

. There is such a thing as a too tought fight that might require an alternative solution (like negociate, run away, etc.). I am not saying this is such a case, but it might be ...
And yes I am not the kind of DM who TPK (at least not on purpose). But sometimes, heroes fail you know, and the way they chose to do does have consequences.
Note that it is cool that you are being pessimistic BTW. And that fight, while probably hard, doesnt look out of your capacities so far.