SO, I checked the website. DH is on Humalog and the website says
"Opened vials should be kept at room temperature or in a refrigerator. Opened cartridges or
prefilled pens should be kept at room temperature."
Here he thougth if it got to room temperature, it was no good anymore.

Luckily this has only happened once with an almost empty pen, so we didn't make a huge mistake!