There is no "too long," especially if it ends up saving a life.
How long is too long on a ventilator/ respirator in this present moment in COVID-19 pandemic? "You make the call"
In the very near future (two weeks) the increase in the COVID-19 death toll will accelerate. This will be due to the number of ventilators/respirators, the critical patient time presently on these ventilators, and the increase in new patients. Note: The reality is some will have to be unplugged.
To help you see the link: https://intensivecarehotline.com/questions/long-long-stay-ventilator-respirator/