Spirit has been on the proverbial ropes for some time now and hasn't made a profit since before the COVID-19 pandemic.  Suffice it to say that there will be more pain for so-called ultra-low-cost carriers. These airlines aren't really low-cost, only low-priced, and that's where the pain is coming from.  

Over the past six or seven years, mainline carriers, such as Delta, United, American, and others have figured out how to compete with the likes of Spirit by developing product offerings, such as basic economy, that strip out all amenities and come in at a comparable price point.  

Price being equal, the big airlines will generally win based on brand recognition and image alone.  That leaves the budget carriers with a choice to further reduce fares and margins, or give up market share - either way, the big carriers are demonstrably winning the fight.  Without a material change in business plan and strategy, a restructuring at Spirit may only delay the inevitable for Spirit and, potentially, other ultra-low-cost carriers.