Its going to take something very special to qualify. My honest feel is ZIM has about 10% chance of making it through. The reason its that low is that while ZIM can definitely upset one of WI and SL, those two teams are still a cut above the rest and would likely win all their other games to clinch a qualifying berth. But if Zimbabwe beats one of WI and SL, they are also equally likely to lose to a USA or Nepal and thats a zero sum scenario. Whilst teams like USA and Nepal are still a notch below ZIM...its been abundantly clear for many years that Ireland, Scotland, and Netherlands are at worst as good as ZIM and on their day slightly better. That leaves zero margin for error, and even good teams can rarely string 5-6 perfect games together.
And thats assuming a team with 4-5 guys aged 35 or older stay fit to give them a full strength squad.
Thus qualification is going to require a perfect storm of SEVERAL improbable events occuring together:
1) Everyone has to be fit and in form.
2) Have to upset at least one of WI or SL
3) Cannot be upset by teams like Nepal or Oman
4) Have to win all games vs near-peer teams Ireland/Scotland/Netherlands
If each of these has an independent probability of 25% you can see that all 4 of them occuring together has a very very tiny probability. And in my estimation, even getting 3 out of 4 means ZIM will get knocked out.