You don't wait for him to take you to court - you'd need to take him. And at the same time you'd want social services involved to back you.
My situation was slightly different to yours - I was the non resident parent at the time (although we close to 50/50 shared care). Ex was drinking to manically depressive state and then overdosing on whatever meds they had to hand (usually antidepressants). Every time ex got admitted to hospital after o/d ing, social services would get notified. But the kids were always with me when ex was getting to that state (but was drinking moderate - heavily when the kids were in their care). But I'd have to keep the kids with me for 2- 3 weeks each time whilst ex recovered from each o/d. I told social services this was unfair on everyone - the kids literally didn't know whether they were coming or going, and I couldn't just drop everything and put my work on hold for 3 weeks every time ex played up (I began to suspect half the reason for it was that ex had realised it was the only way left that they could control me).
For best part of a year this cycle repeated itself, and every time social services intervened they deemed the kids not at risk because they were with with me. Social services continued to support ex through this, and suggested to me that I take legal advice about applying for full custody of the kids. Spoke to a family solicitor who told me I'd got no chance of winning custody battle because social services report wasn't recommending that the kids be taken from the care of the resident parent. Felt like I was just getting fobbed of by solicitor and social services, both passing the buck for taking action.
Eventually things came to a head when ex got hospitalised with another o/d, as usual social services phoned me to check that the kids were ok and in my care. But this time I made the difficult decision to face up to social services and say that I wasn't going to take the kids (they were at school whilst this was unfolding). I had to call their bluff - the only way SS would escalate things is if I wasn't there as the back stop to steady the ship. Of course, I did take care of the kids as needed, but it made ss take things seriously - the next day they told me I had to keep the kids in my care indefinitely, that ex wasn't to have unsupervised access and that I had to apply to court for custody.
I got that in writing from SS, then completed the court paperwork and drove straight over to the court to register the application. But because of the circumstances - I filled in the form to say that it was an urgent application, and I applied for a Prohibited Steps Order alongside the Child Arrangements Order. In the PHO I requested that ex couldn't collect the kids from school, have unsupervised contact with them, or take them out of the county.
I was a bit shocked when the court kicked into action - literally while I was lodging the application at the court admin desk, they noticed it was urgent and within 10 mins I was sat in a court room in front of a judge. I explained it to them, and the judge was fully in agreement with my request, so I left the court with my PHO and temporary CAO for exactly what I'd asked. Week or so later had to go back to court (and ex was served with papers and asked to attend also). This is because the judges don't like to make orders like that without the other party/parent being present.
This time we got a female judge who was absolutely awful - most sexist, nastiest hateful judge imaginable. She couldn't stand the fact that she was having to serve a CAO to take the kids from a mother's care and into their dad's, and she made that very clear. If I'd not got very clear written request from SS for that action the judge wouldn't have ordered it.
Social services continued to be involved (rather than CAFCASS), because they'd had an open case when the court application was made. Ultimately the made recommendation to the family court that kids were to reside with me full time, and ex could have them every other weekend (unsupervised), when she was well enough. I think it was me that came up with the breathalyser request (and I bought and paid the the bloody thing), but for the final hearing the judge wrote that into the final order. Ex didn't like any of it, but because SS had turned on her, she didn't have a leg to stand on so just had to agree to it all. Of course ex blamed it all on social services - 'they had it in for' her blah blah.
So that's why I would strongly suggest you get social services involved. Best way might be to have a word with the school and ask them to make a referral - on the basis that they've observed dad in a pissed state trying to collect the kids from school. You could also ask the school to phone the police if he tries it again (without a court order the school can't not hand over the children to a parent/guardian), and if you end up in any kind of face to face argument with him in a drunk state then you should take the opportunity to call the police too.
The more negative stuff on record the better for your court application. I also had school back me completely in the custody application - SS liase with the school and their investigation includes reports/statements from the school. Their school's safeguarding lead (also my child's teacher), was very critical of my ex in their report.