I think it's important to remember that operating losses owning pro sports teams are a fairly common occurrence, you make it up on the back end when/if you sell the team. Rarely is there a sale that doesn't make an exorbitant amount of $ for the owner. Cuban was just saying the other day how much he lost in operating with the Mavs.
Unfortunately the whole USL system is likely destined to fail unless promotion and relegation is somehow integrated into MLS. MLS will never allow relegation with any of their teams but if they could work out an agreement that allows the top 2 teams in USL to play up in MLS there would be hope for the league. That being said there's a snowballs chance in hell of that ever being an option.