I don't think it's that simple. In general, an employee costs a company about 150% of his salary once you factor in benefits, payroll taxes, disability, etc. If the four remaining pilots accepted the extra flying at 100% or even 120% pay, then making those guys fly extra is clearly better for the company. However, if they all accepted it at 200%, the company would be better off bringing the guy on the street back. At the 300+% rate mentioned earlier in the thread, there's no way the company is better off agreeing to that continually vice bringing back a furloughed guy. Seems to me that the most nuanced approach would be to never accept anything less than 150-200% and then give some of that back to what ever furlough fund exists. That way, the company gets the message through their personnel expenditures, you earn some extra lettuce, and your bros on the street get a little help.
For the record, I'm not an airline guy. I am an occasional part-time math teacher at the local community college.