The first thing that the Crown Prosecution Service has to do is decide upon the relevant assault charge. (i.e. 'common assault', 'ABH' or 'GBH'). They also need to decide whether to pursue any further charges, such as 'threats to kill'.
My guess (based upon what you've told us) is that they'd decide that 'ABH' is the most appropriate charge. Assuming that your ex is convicted of that charge, the court would then need to consider whether 'harm' and 'culpability' fall into the 'higher' or 'lower' categories. If both are classed as 'higher' then it's a Category 1 offence. If only one factor is classed as 'higher', with the other as 'lower', it's a Category 2 offence. If both are seen as 'lower' then it's Category 3.
It seems unlikely that the offence could be classed as Category 3, therefore it's at least Category 2 (and possibly Category 1). A Category 3 conviction can't result in a custodial sentence. The 'starting point' sentence for a Category 2 offence is 6 months imprisonment but a non-custodial sentence is also possible (as is a longer custodial sentence of up to 51 weeks). For a Category 1 offence a custodial sentence is always passed, with a 'starting point' of 18 months and an available range of between 12 months and 36 months. (However, as long as the sentence doesn't exceed 2 years, it's possible that a sentence could be suspended).
Note though that the sentences above can be reduced by a third for an early guilty plea and also that, where appropriate, the actual time spent 'banged up' is only half of the nominal sentence.
See pages 11 to 15 here for further information:
https://www.sentencingcouncil.org.uk/wp-content/uploads/Assault_definitive_guideline_-_Crown_Court.pdf
If 'threats to kill' is added to the charge sheet then the sentencing range is very wide, from non-custodial up to 10 years imprisonment). However the lowest sentences are reserved for single threats that don't really scare the victim, while the highest ones are reserved for people who carry out sustained intimidation against their victims. I suspect that the category used by the court would be the one here which gives a 'starting point' sentence of 12 weeks custody (with an available range of 6 to 26 weeks custody):
https://www.sentencingcouncil.org.uk/offences/item/threats-to-kill/
All of the information in those two links also has to have this laid on top of it:
https://www.sentencingcouncil.org.uk/wp-content/uploads/6.4143_SC_Domestic_Abuse_Paper_WEB.pdf
My own (very wild) guess, based upon reading all that stuff and following court reports for around half a century is that:
(i) the court will decide not to trigger the custodial offence for drink driving (as the more recent offences are unrelated, other than through the effects of alcohol) ;
(ii) the court will class the ABH offence as at the top end of Category 2 and consider a basic sentence of around 48 weeks imprisonment but then reduce that to 36 weeks because of an early guilty plea ;
(iii) a sentence of perhaps 24 weeks, reduced to 16 weeks for an early guilty plea, will be passed in respect of the threats to kill, but that sentence will be ordered to run concurrently with the ABH one ; and
(iv) the court will reject any suggestion from your ex's counsel that the sentence might be suspended.
So my own guess is that your ex will be sentenced to around 36 weeks imprisonment, meaning that he'll be 'out of circulation' for about 4 months (18 weeks).