Even in the extreme weather that Chicago faces sometimes I found they give international airlines a higher priority when they can. I lived there for 10yrs and traveled extensively through the winter. Most recent disaster was last year during the "polar vortex" where it was something like -10°f and blizzarding. All UA/AA outbound domestic and Int'l flights were cancelled a day in advance but my OS flight to Vienna took off on time (had to de-ice twice due to the extreme cold though) but we got out while none of the domestics did. While waiting to board in T5 I noticed LH/QR/EK/AI and others coming in or going out as well. I will mention I did see UA/AA coming IN at T5 from overseas but knew that T1/T2/T3 were at a standstill, not even letting people in because it was all cancelled.