You just started counseling and want to tell him it's over before giving the therapy a chance? This is not the way to think this through unless you are already done and are only going through the motions.
He may not be ready to consider stopping drinking. He may not care if you issue the ultimatum or not. He may not think he has a problem, sort of like not everyone who drinks is an alcoholic.
What I'm trying to say is this:
When we are more vulnerable, under the influence of alcohol or drugs, our mouth is able to spout off stuff we normally keep to ourselves. Being a guy, he probably holds a lot of stuff inside and does not have a healthy way of getting it out of his system. Therefore when the alcohol loosens his lips, things spout out that he normally represses. They are not always the real thing he is thinking/feeling either.
When kids are mad at us they yell they hate us, their mouth is working without the benefit of their filter keeping the stuff inside. They don't really hate us, they are angry and hurt. They are saying the worst thing they can think of to try and hurt us emotionally because they are hurting emotionally and blame us.
So, I would say give the therapy at least 6 months, with him and you both going jointly then perhaps some private too. That way you can each work on things for yourselves and then the relationship as a whole too.
If, after 6 months, he is still feeling the same way and not benefiting from the therapy talk to the therapist about the ultimatum. They may be able to say with some familiarity if it will work or if finding an attorney is the next step.
I think that marriage counseling is a big deal and that many times it takes a while to see a big change. I would give it as much time as possible.