F9 would have to take NKs $3.3B in debt, including a $1.1B secured debt payment due in less than a year plus another $500M due in 2026. F9 has about $650M cash on hand according to their last 10Q filing. The combined entity would have $7.4B of debt which makes it even more leveraged than American, compared to total revenue. Spirit only has cash on hand because it sold planes this year. NKs debt is rated as "junk" so refinancing it would be at very high interest rates, probably higher than a combined F9/NK profit margin.

If F9 acquired NK as an operating airline it has to cover NKs operating cash outflow problem as well and would likely run out of cash before any merger synergies can be attained.

The best thing F9 can do is see if they can purchase assets in BK at a discount rather than taking on any of that debt. Unfortunately they will have to compete with other airlines that have far more cash for those gates and planes.