Break formation bug?

[Q]

"Was the leader, the base eliminated?"

No.
Unfortunately against the vastly superior enemy in this case the optimum firing range with break formation was letal to the ships. If they had stayed together with the bases they would have survived and inflicted huge losses to the attacker. And tactical combat was not a reasonable alternative with a total of about 600 ships involved.
Strategy is defenitely something that should be improved for SE V.