I'm sure that you can use air in a shock for a temporary and probably for a permanent fix. I have owned air planes for 22 years and just sold my last plane. We prefer to use nitrogen in the shock struts, but air is OK, especially if it is dry air. The main reason for nitrogen is if something can get really hot, like in the tires of a jet where oxygen can be a bad thing. The main reason for not using air in the struts is that air compressor air may have moisture in it which could cause internal corrosion. However, if it is an emergency fix, air will be fine, it is, after all, 78% nitrogen. So, if you had seals and the skills to fix it, and a high enough pressure air compressor, that would do the job to finish the trip.
I have really enjoyed this story and Walter's other trips as well. Really good stuff.