Niflheim was concerned about Izroth, who had been out of contact under the lake for roughly thirty minutes.
However, there was no time or breathing room to formulate and execute a feasible rescue plan; therefore, Niflheim resolved himself to face the worst possible outcome.
As the party's leader, Niflheim understood that he had to set aside his personal beliefs and eventually confront the facts—there was a good chance that Izroth would never resurface from the lake!
If that were the case, it would be up to them to defeat the Hydra with one less party member.
The good news was that they discovered the Hydra's regenerative abilities were not infinite, which was likely caused by the creature's weakened sealed state.